If you're running the original 3-speed transmission, that's the weak point. I'd suggest a turbo 350 or 400, with a few performance upgrades like a slightly higher stall speed torque converter. If you insist on staying with a manual trans, (a BIG mistake) try a Saginaw 4-speed, or one of the heavy-duty 5-speeds intended for service behind a V-8. The popular T-5 swap probably won't handle the power and torque of a beaned-up 350.
Jerry
