The engine I've located does need a (partial) rebuild.

Heads are good, but the bottom end needs a rebuild.

Here's the plan to get some more juice. Bore out. New Pistons. Performance cam. Split Manifold and Dual Intake.

What is the biggest bore out it can get to(and still be stable)? I've heard 301 CI.

Any tips to squeeze out more juice?

Thanks for the sage advice.