Originally Posted by DaveK2
Is there a way to convert the transmission or do you have to put a new one in?
You can convert an SM420 4-speed using parts from a bigger or later truck. I don't believe a 3-speed can be changed.

1955 1st GMC Suburban | 1954 GMC 250 trailer puller project | 1954 GMC 250 Hydra-Matic | 1954 Chevy 3100 . 1947 Chevy COE | and more...
It's true. I really don't do anything but browse the Internet looking for trouble...