i know this would be hard to determine, by what specs i have but i was given a 454 in trade that i don't know much about & was wondering if any engine gurus would be able to chime in....454 is a 1975 block (361959) heads are 3904390 with competition roller rockers 1.72 ratio, performer rpm air gap intake, 750 dbl. pump holley & 2 inch hooker headers....i did do a compression test on this motor (cold did not run for a year, carb wasn't tied wide open) & got 175lbs in every cylinder...my questions are by those numbers i'm thinking pistons must have been changed to achieve that much compression?...anybody want to chime on approx. hp & tq....also any idea on specs of cam with that compression.....i know this would be hard to determine...but maybe somebody with expierence with big block chevys would care to guess? thx for any replies

Those heads are small valve closed chamber 396 heads; that's why the compression is fairly high.

HP would depend on whether bigger valves have been installed and the cam specs.

Without knowing what cam,..

With:

Factory oval port heads (guessing,..hopefully they'e not peanut port truck heads),
9:1 CR (guessing,..in 75 it could have been lower),
RPM Intake
750-DP
2" Headers
(Roller "tips" or full Roller "rockers"?)
Good compression and well tuned engine,..

...I'd say roughly 400 HP at the flywheel,..maybe 425 depending on the heads.

The part numbers you list for the block and heads don't register with me or my book, 'Chevrolet by the Numbers', by Alan Colvin. You might do a google search to find out the pedigree of the heads and block.

One website said they were 66-67 396 heads.