I just rebuild my mark IV 454. I stroked it to a 496 using forged Scat kit which included H-beams and all the bearings. I used probe forged blower pistons, had a custom cam ground (for marine applications) and am running a B&M 177 blower with a demon carb. Should put out a reliable 600-650 hp on pump gas (low compression like 8.5:1 or so). I am just using hand ported 781 heads with 2.19/ 1.88 valves and had the exhaust changed to hard etc. My blower puts out 5 psi so it won't kill my marine engine which will live most of it's life in the high rpms and on the boost the whole time.