The Stovebolt Site Forums The Parking Lot '60-'66 Trucks 3 speed to 4 speed conversion

How difficult is it to convert the 3 spd column to a 4 spd SM420? Is it simply a matter of swapping the tranny hump access or is the floor and firewall completely different?

The primary & secondary transmission humps for the high hump are the same and the same is also true for the low hump, but both the primary & secondary covers must be changed, since the primary & secondary covers are not interchangeable. The automatic & 3-speed transmissions were low hump and the 4-speed transmission had a high hump.

Thanks, I just found Jolly's how-to on the GMC6066 site.