The '57 should be an SM420 if its a 4-speed. That transmission was used until sometime in the '60s.

Be aware that the '57 had an open driveline, and your '46 would not.


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...