Bringing everyone up to speed. Son's engine dropped a valve and engine needs to be rebuilt.

I got a complete 1954 235 with clutch housing that I think we will have it rebuilt and use the 1954 in his truck.

What year did they come out with the 4 sp synchronized
transmission and what years would it be a direct swap to the 46 truck with a 54 engine?

Also years ago I had a 1950 F 1. My dad and I found a Junky that had milk crates of straight 3 sp gears. However they were all straight cut. My trans was synchro with helical gears. The proprietor said that those straight gears would fit if we switched all the gears. We declined because we knew where new helical cut gears were for sale.

That made me think can later GM 4 sd synchro transmission gears fit into an earlier GM non synchro transmission housing?