Building a BBC to make 700-800 HP "with compression" will not require a blower. In fact, if CID is over 450 or so, a 6-71 will slow it down... An 8-71 MIGHT work a bit better, but a 14-71 is truly"full race". By today's "standards", a 6-71 is a street component.
Stroke it to 496. Use the best heads you can afford. We "like" Brodix and Dart here. If your budget can "stand" it, go for a "spread port" head like Big Chief or Big Duke. If not, stick with the aforementioned brands. Avoid "price" shopping. You can't get "the good stuff" cheaply. Since you want to supercharge this engine, be sure ONLY a high quality porter does your heads. Contrary to popular belief, port work is MORE important in blown applications than in N/A engines. It doesn't need to be much "bigger", but the paths need to be clear and relatively smooth. Each obstruction will inject significant heat into the mixture, costing power and efficiency.
We have success with Eagle rotating "kits", but have heard of others having dimensional issues. For imported engine parts, Eagle is the best (IMO). Their 4340 cranks are VERY nice, and TOUGH. Use the longest rod that will "fit". For power levels over 1,500 HP, we need to talk... (:-
You might also consider a mechanical injector over the two 4-bbls. Enderle is currently the hot lick along with Waterman. These are especially effective when running methanol for fuel, but do offer far superior performance over both carbs and EFI regardless of fuel type.