A bigger valve doesn't always equal more power. I will tell you that the little 2.190" valve on the TFS heads with the small 170cc port will support 700 hp easily. Cramming a large valve in a cylinder doesn't always mean it's going to do better; it could shroud the valve and then you have larger problems.
Those TFS heads on a pump gas, hydraulic roller 390 will make 540 hp. Those TFS heads on a pump gas, hydraulic roller 445 will make 550 hp and almost 590 lb-ft of torque. They will also make almost 700 hp on a 465 bracket race engine. They are good parts.
To the OP, I wouldn't worry about the ProMaxx heads. They are Chinese copies of an Edelbrock. The Edelbrock FE head, IMO, is defunct these days with all the other offerings available.
I also wouldn't spend a lot of time disassembling, cleaning, etc, etc. You will find yourself jumping into a rabbit hole that doesn't end. What happens when you pull the pan and see that the crank has some journal issues? Do you grind? When you're looking at grinding or repairing, sometimes it's more cost effective to buy a new crankshaft. Do you recondition the rods? Change piston rings? New bearings? I would completely leave it alone and use it for a *temporary* engine.
I also wouldn't worry about any sludge or gunk.
Last November, I picked up a 1966 352 FE core engine. It was complete from carb to
oil pan, so I decided to have some fun and dyno it. It made 208 hp with the factory 2 barrel carb and intake. Pulling the PCV valve out, adding in 42° timing and bolting on a Holley 500 cfm 2 barrel got me to 234 hp. I swapped on a Blue Thunder 1x4 intake and a 600 Holley for giggles and got 264 hp. It had great
oil pressure, ran like a top.
Here's what it looked like inside:
Bottom line is, if it's a temporary engine, leave it a temporary engine. Too many guys tear down temporary engines only to make them complete engine build projects. The cam is already broken in, rings seated, clean it up as best you can with a shop vac in the lifter valley, get it running, change the
oil, and then whoop on it. Best time you'll ever have because you don't have to worry about an expensive engine.