Aye, 500 hp may be a lot to ask for from a 350 on pump gas, but a 454 should handle it no problem. We're only talking 1.1 hp per cu in. It would require 1.43 hp per cu in to make 500 hp from a 350. You could always get a 496 crank out of one of the late model 8.1 engines, toss it in your block, and then you would need only 1 hp per cu in and that is a very reasonable power output on pump gas. With 496 cu ins, your engine is very close to GM's 502 and I would just copy the 502. You may be able to throw in a bigger cam and increase the compression ratio over the GM setup to make around 550hp on pump gas.