Ok. Definitely need exhaust manifolds for sure.
If it's the crank I wouldn't bother man, I hear it's not worth saving a later 70's olds block, is that true? 🤷♀️🤣🤣🤣
Upper engine noises were common, never personally had issues with rocker pivots but yes was an issue.
Cracked flex plate can imitate sound of bad/noisy lifter.
As far as rebuild on older Olds..., personally I like to save what I can. Not a hoarder, but after Afghanistan was kind of like therapy to do something constructive and have it come to fruition.
Plus I'm more into the sound of a cammed V8 than into hearing a blown twin turbo 4 cylinder running nitrous on a flat plane crank.
So anyhow, depending on your location and what's in your area or your comfort level... You can go LS Swap, Crate SBC, or repair what you have and try to keep original.
Being that it is a Delta 88 I would be more inclined to fix the 350 or Replace with 403 or 455.
The 350 is definitely worth rebuilding IMHO. It's greatest limitation of cost containment is the lowered support at this specific time. Intakes are about double, overall quantity of cam profiles are less, aluminum heads are more in dollars, but less in variability and availability as compared to SBC.
But to think... A Real Delta 88 with a Real Rocket 350!!!