I can offer this.. building a 500 hp motor is achievable but then you need to consider a chassis that can survive and use that horsepower! And more important stop that horsepower!!

The more performance you want to achieve, the more it'll cost. Since you have no clear set goals yet. I'd suggest doing a "more vanilla" overhaul so you can still have your fun and since you're set on a big block you can still make lots of torque/hp to get your blood flowing.

It is that old saying, Speed costs money, how fast can you afford to go???