Set of stock stealths milled to 75cc I'm looking at.

engine 1. 383, .030, old low comp pistons, ~0.088 in the hole, .020 steel shim gaskets, comp 268H, efi plumbed rpm perf intake. Currently has 78cc 516's with 1.74 exh and a simple unshroud of the bigger valve, 1 3/4 headers, 2200 stall, a-500 with 3.91's.

#2 late 70's 440, stock rebuild with low comp pistons, stock rebuild 452's. Would use the stealths and a cam to build cyl psi (mp528 maybe?) Would look to go bracket racing with it and hope to run 11.99 with a 3600lbs car (with driver), 4000rpm stall, 4.56's.

What HP increase would each see?
Is there something thinner than the .039 felpro that works with the stealths?

Trying to do something on a budget, either make my Fury faster or get my Coronet running again. I've got several serviceable short blocks, just low compression unfortunately. What I don't have is a decent head right now, and these pre-milled ones popped up, but the calculators aren't giving me the CR I was hoping for with 75cc chambers.