Well if I can get my stock 390 block with an addition of 427 cross bolted mains on it to handle 800hp, then I will keep the 390 block and stroke it with the 445 stroker kit from survival.

As for the supercharger, if I go too small like a 6-71, I'll build boost at low rpm but if it is too small it will drop off in high rpm and create alot of heat. If I go too big like a 8-71 it might be to much and not create power at low rpm.
I contacted superchargerusa.com and explained my build and they suggested their "Large Bore 6-71" It is a 6-71 with I believe a larger case, so its like an inbetween of the 6-71 and 8-71.