[rotorwrench]

The synchro is the early type that was used prior to 1939. It won't work with the later input and main shaft. Study up on Mac's book. You can use all the later gears in any of the early transmissions but you can't go the other way when you need the later type main output shaft for open drive. You will also need the 91A type shifter fork set up in the top housing too.