Cometic makes one for the Yates heads but I'm unsure of the fit. 
The M6049-A3 head is a high port design. 
Fel-pro 1229 should work for you. 
https://www.jegs.com/i/Fel-Pro/375/1229/10002/-1
From the Pantera site:
The original intake gaskets for A3 heads were Ford Motorsport M-9439-A341
which are no longer available.  Fel Pro makes two intake gasket sets for
the Motorsport high port heads.  1229 is listed for A3 heads but the port
opening measures the close to C302B heads (1.35" x 2.20").  1265 is listed
for B351 and C302B heads but the port size is listed as 1.35" x 2.22".
Both as "trim to fit" for the A3 heads.  I know that p/n 1229 has round
holes on both ends in case you run coolant through the intake.  I'm not
sure about f the 1265 have the same holes.  Both 1229 and 1265 of those are
0.060" thick.  Fel Pro makes similar intake gaskets in thinner (12531 is
0.030", FEL-12532 and 1253S2 are 0.045") and thicker (12535 is 0.120")
sizes for Yates heads that could probably be adapted if you need to
compensate for head or intake milling.
This site will give you an idea of the port differences: (Approx mid-page the heads are discussed)
www.the351cforum.com • View topic - 403C with A3 Ford Motorsport aluminum heads
M6049 family specs:
Part CC's Int Exh Int Exh Description
Number Port Port Vlv Vlv
Vol Vol Dia Dia
CC's CC's In In
M-6049-A3 62 241 134 2.15 1.71 optimized for 355 cid
and larger, drag racing,
circle track, etc.
M-6049-B351 62 223 106 2.15 1.65 optimized for NASCAR
M-6049-C302 62 212 95 2.15 1.65 optimized for Trans Am,
320 cid and under
M-6049-C302B 62 212 95 2.15 1.65 designed to permit 
custom porting, not 
legal for Winston Cup
M-6049-C3 62 212 95 2.15 1.65 designed to permit 
custom porting, not 
legal for Winston Cup
very similar to C302B 
M-6049-D302 62 212 95 2.15 1.65 same as C302 w/o port 
throat machining or 
valve seats/guides
M-6049-D302B 62 212 95 2.15 1.65 same as C302B w/o port 
throat machining or 
valve seats/guides,
not legal for Winston 
Cup
A3/B351/C302/D302 Head Notes:
----------------------------
1. The M-6049-A3 head has the largest intake port volume (241 cc's)
and exhaust port volume (134 cc's), intake flows 280 cfm @ 25 in Hg 
as cast, doesn't respond to rpm transitions as well as B351 or C302, 
has slight bend on intake port wall to accomodate pushrods, raised 
floor increases port radius, straightening the turn for incoming 
mixture and minimizing fuel separation, optimized for 355 and larger, 
drag racing, circle track, etc.
2. The M-6049-B351 has intermediate port volumes (223 cc's intake, 
106 cc's exhaust, flows 260 cfm @ 25 in Hg as cast, intake port 
wall filled around pushrod area to straighten it, intake floor same 
as A3, material added to exhaust port floor increasing radius for 
flow, optimized for NASCAR.
3. The M-6049-C302 has the smallest port volumes (212 cc's intake, 
95 cc's exhaust), at the radius the intake port floor has been 
filled about 0.120" which forms a slight hump to lift incoming 
mixture and drop it evenly around the valve, like B351 wall filled 
around pushrod to ensure straightness, optimized for Trans Am 320 
cubes and under, narrow ports for increased velocity.
4. B versions (M-6049-C302B, M-6049-D302B) were revised for durability 
but not approved by NASCAR, advertised as "too hot for NASCAR" by
SVO, extra material in rocker pedestal area and at spring seats,
rocker cover raised 0.2", improved heat treat, shoulder added to end 
plug for improved sealing, outer bolt boss height raised to provide 
common head bolt length.
5. All versions are fully compatible with 302 Boss/351 Boss/351 SVO 
valve train parts (will accept 2.19"/1.71" valves) and have cast 
iron seats and guides (titanium valve compatible), rocker stud 
pedestals are machined flat and holes are tapped for threaded studs 
and guide plates.
6. Uses Motorcraft AG-series spark plug (14 mm, 3/4 inch reach) with 
gasket.
7. Head is cast with combustion face and front and rear coolant outlets
to allow use on 351W and 351C blocks. Pipe plugs are provided to 
seal openings as needed. On Clevelands, install pipe plug in holes 
on end of heads.
8. Originally referred to as Phase 1, 1 1/2, 1 3/4, and III heads.
9. Brodix has recently introduced a bolt-on replacement for the C302B head.
10. Nominal combustion chamber volume for the high port heads is usually 
listed at 62 cc's, though Ford Motorsport sometimes lists 65 cc's.
11. Special versions of these heads were made for certain race teams.
I have a set of narrow intake port A3's, for instance.
12. High port heads require one inch longer head bolts or studs. If using 
head bolts, also use hardened washers. A3's, B351's, and early versions 
of the C302 heads had one short bolt. Later C302B's got common length 
bolts.
13. High port heads were designed to fit both Cleveland and Windsor block 
and come with combustion face and front and rear coolant outlets which 
get plugged with aluminum pipe plugs as needed. Where the plugs go is 
a function of the block, whether or not the intake has a coolant cross-
over, and whether or not you run a remote coolant cross-over. For 
instance, if you put high port heads on a Windsor style block with a 
coolant cross-over manifold, the plugs go in the ends and the 
combustion face and a 0.8" hole is drilled at the coolant cross-over. 
The supplied instructions illustrate the options. Use a thread sealer 
and make sure the plug is below or level with the deck surface. On 
Cleveland blocks, pipe plugs go in the holes on the ends of the heads 
(coolant goes from block to head, intake is dry). Also an external 
(not in manifold) coolant crossover can be used to take water out the 
front of the heads.
High Port Family Gasket Notes:
------------------------------
Head Gaskets
M-6051-A331: Blue Fel Pro headgaskets for A3/B351/C302 heads on a Windsor 
block. Does not have the round water transfer hole required for a 
Cleveland block, otherwise same as A341. For 4.0" bore (and likely 
overbores up to 4.060"). Solid metallic core with wire encased combustion 
seal for competition application. Surfaces are coated with Teflon. Do 
not use sealer. Can be used with iron Cleveland heads. 
M-6051-A341: Blue Fel Pro headgaskets for A3/B351/C302 heads on a Cleveland 
block. Has the one round water transfer hole required for a Cleveland block, 
otherwise same as A331. For 4.0" bore (and likely overbores up to 4.060"). 
Solid metallic core with wire encased combustion seal for competition 
application. Surfaces are coated with Teflon. Do not use sealer. Can be 
used with iron Cleveland heads. 
M-6051-B331: For A3/B351/C302 or iron Cleveland heads on Windsor block.
Same as M-6051-A341 except has bifurcated (enlarged dual) coolant transfer 
holes added for improved cooling and upper front coolant hole deleted so 
Cleveland or A3/B351/C302 heads can be used on Windsor block.
M-6051-B341: Same as B331 but for blocks bored to up to 4.125" (Fontana, 
Dart, or Ford Motorsport race blocks). Bore flange valve pockets have been 
added to unshroud intake and exhaust valves. Unique right and left hand 
gaskets.
Note: Both B331 and B341 can be used on Cleveland blocks if modified per 
supplied instructions.
Victor Reinz and Cometic also make high port compatible headgaskets.
Intake gaskets:
Fel Pro p/n 1229: A3/B351/C302B heads with 1.83" x 2.20" port opening 
Notes: Black material, comes with tube of black RTV, rubber O-ring, 
pair of intake manifold gaskets, and instructions, no end seal rails 
(make out of cork or use RTV... I prefer cork). Can be peened to size.
The tag on the Fel-Pro part number 1229 gaskets state they are for A3 
heads but this is incorrct as the port dimensions are listed (and measured) 
as 1.83" x 2.20" which fits the C3/C302/C302B heads. Note that p/n 1229 has 
round holes on both ends in case you run coolant through the intake. Also, 
1229 comes with a tube of black RTV but no end seals. There is a separate 
part number for wide port A3's (1.83" x 2.65") though you can use the 1229 
gaskets on larger port openings by placing gaskets against the head and 
tapping with a ball-peen hammer around the port opening to get the desired 
port size. Note that many C302B's are ported to a larger gasket size, so 
the Fel-Pro catalog lists port dimensions. The Ford Motorsport M-9439-A341 
gaskets have the correct wide port opening for A3 heads but I think they 
are no longer available.
Exhaust gaskets:
Fel Pro p/n 1417: A3 cylinder heads (1.94" diameter round port size)
Fel Pro p/n 1431: B351/C302 cylinder heads (1.81" diameter round port size)
Fel Pro p/n 1433: Yates cylinder heads (1.86" x 1.68" port size)
Valve cover gaskets:
High ports heads use standard 351C valve cover gaskets. Fel-Pro makes part 
number 1636, a thick three layer (cork-metal-cork) valve cover gasket which 
improves clearance if you have issues with roller rockers to valve cover 
clearance.