Re: 454 power level?
Without knowing what cam,..
Factory oval port heads (guessing,..hopefully they'e not peanut port truck heads),
9:1 CR (guessing,..in 75 it could have been lower),
(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.