That's a bit much for a hotrod, specially for a 15 year old, I'm 16 and I even think that's to much for me. That's even if the big block will fit in the car you want, you are going to have to replace entire drivetrain and front clip. Weiand sells good superchargers, you would need a 871 for a BBC and a 671 for a SBC, they run around $2400. That 425 HP is crank HP so once you subtract all the % for the amount of power that the tranny and rear end take up so, your looking at approx 400-415 rwHP with the 425 crank HP, nobody needs 500 HP, you should probably take it safe and build an engine that makes 325 HP and then keep putting new engines in that make about 100 hp more than the last, this way you will be able to get used to the power so you don't wreck it cause you coulden't handle it.