Cuda 620 your a Chevy lover. I think the right 408 with aluminum heads and some measures to shed a little weight would walk all over your sorry heavy Camaro. Or how about a new 6.4 stuffed in a a-body- same result.
Looked into the A body hemi, 5.7 ,6.1 , 6.2 and 6.4. Not worth the bang for the buck or difficulty for that matter. Actually easier to do an LS with a 2004R or a TKO600. Plus parts and cost and support.