I had 454 built to the 420 specs but with large oval port heads. I built a 454 stroker to a 496 9-1 cr. balanced blueprinted, a custom grind comp cam with the 4-7 swap 551in/.557ex; I had the large oval head valves replaced with 2.25/1.88 11/32 stems ported and flowed; I am running the same ign DUI, the same intake with a 1" spacer eldelbrock rpm air-gap but now I am running a 850 sea demon and revolution exhaust no mufflers. The engine now pulls hard low and midrange, but the top end is flat I can turn about 52-5300 rpm with the same prop I had last year 24 bravo 1 labbed; I would think I would have more power on top also. In another word the boat is the same on top as last year. But now it is much, much quicker.