'71 318 compression...

302 heads would be great for a teen with bolt on parts. Another option might be to take the heads you have do some home porting on them and re-install with a thinner head gasket. won't break the bank.

Another thing to keep in mind would be your exhaust, if you still have those stock 318 manifolds I don't think you would gain much by improving head flow. Those 318 manifolds would be the current bottleneck in the system. I had pretty much the same setup, but had manifolds. Switched to headers and it gained gobs of power. It was like the icing on the cake so to speak. there are a few options for better flowing manifolds or headers if you have stock 318 manifolds.