Degree the camshaft. I didn't see where that was done. I would install it down about 106 ICL. That's 2 degrees advanced from the cam card, but it has low static compression and that'll help. Then, get you a good hot ignition curve. Something on the order of 20 degrees initial timing, 36 total and all in by 2500 RPM. That will turn it into a tire frying beast and all you will have done is labor and maybe an advance spring kit and an FBO limiter plate. Cheap cheap. ALWAYS be leery of advice like "get new heads" or "get different pistons". Most combos can be made to haul *** with some tuning. You just have to know what to do.
