The biggest deficiency those 70's vettes had was the compression ratio. The only way to raise the compression ratio without pulling the motor would be new heads. Look for some closed chamber heads or some similar aftermarket pieces, try to get your ratio up around 9.5:1. That could get you in the 400+ hp range if coupled with the right cam. Of course, you will have to change the manifold and intake to match the heads and cam. That Qjet flows 750+ cfm, but a lot of people prefer to go with the Holley or Carter. They may make a little more hp with better throttle response, but who cares about that with gas prices as they are.