You can make 440-450 FWHP & over 500 lb. tq quit easy with those 781 heads & a smaller FT Hyd. cam, But the compression needs to come up to at least a true 9.1, It can also be done with stock 781s, This is my combo & i'm at 450 hp.
.070" 454 445 block.
Probe 18cc dome pistons, 9.51 compression.
Stock 781s with Perf. VJ
Lunati FT Hyd. cam, 527/553, 224/234 @50, 112/107
Air-Gap intake, 950 carb
1.3/4" headers, HEI ignition.
If you do up the 781s with the larger valves with back cut, Bowl work & short turn, Drop in either a moderate FT Hyd. or milder Solid, 850dp, It will make over 500 hp easy.