Intake manifold problem

[MOTORHEAD]

I've been having problems with my FE 452 shelby block based engine since shortly after it was installed about 10 mo's ago. Induction was a used set of webers purchased from a CC member. The carbs were in fine shape, and are the Bologna units. It ran well initially, but developed a intermittent missing at cruise which was traced to oil fouled plugs on the left bank only. Valve seals were changed with no inprovement. Put UV dye in oil and found oil comming past the int gasket on the left side only. Pulled intake and installed different gasket set-up , but still had oil fouled plugs. Decided it must be the manifold, even though I had checked it before installation.
Not having another weber manifold to try, I installed the BT 4bbl manifold that was originally on the engine along with a Demon 750 DP carb I had laying around.
WOW ! what a difference ! No plug fouling, engine will idle for a long time w/out fouling plugs, very stable operation, BUT----- it feels like It's down about 100 hp !!!!
However it did confirm that the weber intake was the problem all along. Don't think it's worth salvaging because it was ported and milled before I got it, and there's not enough mat'l around the ports to ensure a good seal, so the hunt is on for a good used manifold ( or smokin' good deal on a new one) is on.
While the 4 bbl is on, I'll get the car on a dyno, and then again after the webers are back on.
The engine is cammed for webers, so it's not optimal for the 4bbl, also initial timing is at 22 deg, wondering if thats ok for 4bbl, or should it be lower ?