700HP 383 Buildup

Why not build a 500 HP 383 and then toss a 200 HP Nitrous kit on it? Just make sure you build the motor with Nitrous in mind. 500 HP is do able and 200 hp nitrous is livable. If you get some indy heads or one of the other aftermarket ones you'll probably get even better numbers.
You could also stroke it. toss in a 440 crank and have a lowblock 426, or even a bigger stroked crank.
A 400 block would be better though.
Good luck