small block chevy

I just picked up a 307 Chevy not Olds thinking it was a 350 the guy told me it was a 350 and I looked up the casting Numbers (3970024) comes back to a 69-73 Chevy 307, either way, I want to Put it into my 81 Monte Carlo 229 v6 I know I need to replace everything but my goal on the 307 is 400hp...