A 1950 model used a two lug synchro. 1953 and 1954 used a 4 lug synchro. 1955 and later was different again and will not work in the earlier cases. However, two of the lugs can be ground off and make it work in a 1952 and earlier. It has been a long time since anyone sold these. Occasionally they appear on eBay and sell in the $300 to $400 range. The brass synchronizer rings were available to rebuild the synchronizers at on time, but I think that has been a long time. Passenger cars used the same synchronizer. I would watch eBay or tear a bunch of old 3 speeds apart and maybe you will find a good one.
