I think that if both transmissions are set up for an enclosed driveshaft, you can use the three speed universal joint with the yoke of the 4 speed.
The speedometer drive gear in the four speed will give you an incorrect speed/miles because the rear end ratios are different I believe. A speedometer shop can fix you up with a little external compensating gearbox.
I put a '49 four speed out of a 3600 into my '51 half ton many years ago.
Kurt
