I really can't give an unbiased opinion on the motor issue since i have a 429 in my truck but with all the aftermarket parts out there; 392 stroker kits, aluminum heads, etc; it might be easier than i think to get 500+hp out of a 351. On the C4, you woud be surprised how much a well built C4 can take. With the right clutches, band, servo, shift kit, etc. they can take a good shot.