6-speed Trans Modification
Short answer: Yes, you can fit a 5- or 6-speed (or an overdrive auto like a 700R4/200-4R) — the big payoff is highway mileage (a 700R4 behind a 310 hp 350 returns ~24 mpg). It won’t hurt value, especially overseas, and you can keep the original 4-speed to sell with the car.
Look for a transmission with the universal B-O-P bolt pattern, or use an adapter plate to bolt a Chevy bellhousing to the Pontiac motor. Measure carefully; if you must cut the tunnel, cut cleanly with a thin-blade saw and save the piece so it can be welded back for originality.
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Content last modified: June 13, 2026 at 10:06 am
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