I don't know why your stuck on rpm, everyone knows your gonna have to spin it, I don't think it would take 8000+rpm as you 1st said, My guess it would around 7000 rpm probably fall somewhere 6700-7300 maybe 7500 at most. VE% and CR play a big roll, take that 477 hp 318 bump up the CR from 10:1 to something like 12.5:1 you'd have your 500 hp and CR isn't gonna raise the rpm if anything might lower it a little since where running a more efficient engine, Sure we don't have any 318 eg.. but look at 5.3ls or 302 even 340 it's not gonna be much different from those engines took to reach 500 hp, The video of the Ford and Chev 302 made more than 500 hp, Ford 302 520 hp @ 7000 rpm and Chevy 543 hp @ 7300rpm, if those engines where cammed to make 500 hp they probably would at slightly less then 7000 rpm or at least at 7000 rpm to, 318 has at least 16 cid on those two engines depending on final bore. So the formula is to put heads on that can support 550 hp or better and add a big cam and 10 - 12.5:1 cr and spin around 7000 rpm and call it a day. Sure you could do better with a 408 etc.. but you could always add a 4" stroke to a 318, 318/360/340 bore isn't all that huge in difference, does it matter yes but unless your shooting for 500-750 hp + on a high competition race engine, for the average street, street/strip engine 318 can take all the same parts including cranks. Saying that yes it makes more sense to start with a 360 block or even a 340 one if you can find one at a reasonable price and add desired parts and stroke.