I recently picked up some bbc parts that were on an HP500 motor. I bought everything except the block. Going through the heads which are GM iron heads 088 castings. I found numerous broken valve springs destroyed shims but the most troubling is serverly pitted exhaust seats and valves. I was told these parts came from a running hp 500 with 200hrs or so. Both heads at #7 and #8 cylinders have serve pitting on seat and valve one a little worst than the other. I assume reversion or some kind of manifold leak or gasket. Is this common and these motors?

HP500's had reversion issues, and valve spring issues. Not surprised at what you found.

Well that explains all the pitting on the exhaust valve and around exhaust seat. Both will need replacement. The only thing I wonder why only the back two cylinders? All other combustion chamber seats and valves look great.

They're the closest to the exhaust tips?

Just finished spot,peen one head definalty going to need an exhaust seat not sure if it can be savaged. Along with my many hp500 parts I was cleaning up the pistons and started measuring the rings and a bit confused. Top ring 2 mm second 1.5 mm oil ring is 3/16 what! I can't even buy a set with that arrangement from JE. Anyone else run into this also oil,ring width is .107 which is a lot thinner than they spec ?????????

Any part numbers on the pistons?

Port them