I’d just build it as a 572, knowing the heads are holding it back and that you’ll likely need something bigger to get into that 850hp zone.

I did one a few years ago....... it was about 870hp with a 440-2/w-4500 adapter , 1150 carb, 14:1, cnc345 Heads, 1.7 rockers, .782 lift cam.

Over 900hp with a TR.

68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads