Gelee, the casting number you gave is listed on two websites (
this one and
this other one ) as belonging to an SM420 4-speed.
It's my understanding that the newly synchro'd and helical-geared (except 1st and reverse gears) SM420 first appeared in 1947. However, the 1954 master parts catalog shows this particular casting number as belonging to the case for the earlier (and non-synchro) '31-'47 4-speed. So there is a bit of a contradiction here.
This casting number also came up in an earlier thread on this forum (
see here ). The consensus there was that it was the earlier tranny. Those two websites I gave above are probably mistaken.
It may not be hard to swap in an SM420 if you really want a synchromesh tranny, but I'll leave that determination to those who might know better than I.
Anybody know the moniker for the early 4-speed?
