My experience with the 22RE exhaust manifold:
Had an exhaust leak, tried tightening rear studs, they pulled out of head.
Took off manifold, it was warped, so I needed to get it surfaced so it would seal.
Then because I'd lost 2 studs holes, I drilled out all the holes and put in threaded inserts so there was no way they'd pull out again.
And because I'm thrifty, I used SAE instead of metric ( 3/8 vs 10mm) and cut to length a stainless steel threaded rod instead of studs. (and stainless nuts).
This is a low torque application, so you don't need grade 5 or 8, and stainless is stronger than grade 2 (close to 5) and it won't corrode.
