Engine ID for Correct Parts

[Skidmarks7D1]

Hello! I bought a 71' C10 a few months back. It's been well taken care of and runs great. I drive it almost daily with zero problems. The guy I bought it from builds trucks, but did not this one, just some adjustments. He did not have a lot of info on the truck previously to him, only what he saw. He gave some info he had, and lots of spare parts he collected for it, mostly cosmetic.

I did know about an exhaust manifold leak when I bought it. Its a little noisy and gassy in traffic, but other than that so far no problems. It will overheat the starter and has friend the nearest cable once.

I'd like to start replacing some older parts that I know will fail, including the manifold. I've got a muffler guy locally who said he'd gladly replace the mani and pipes up to exhaust can for about $100, i'd just have to track down the part.

The engine VIN # is V0331FC which tells me its a 69' Corvette? The seller told me it was a 350.

The existing mani ID's are
PS:
3896956 which searched at 67-68 283, 327
DS:
3932469 which searched at 69 - 70 327, 350

Does anyone have any suggestions as to:
1) What engine is in this truck, perhaps how to further ID it. I have searched the block for additional info, but no luck.
2) Should I replace both exhaust manifolds? I am leaning to yes. It seems like the ones in right now (one has a crack in it) do not match.

Thank you all again for your help!

Cheers