There are several variations. The early transmission with the multi plate clutch has a different input shaft, as the clutch is mounted to the shaft, not the flywheel. It also has a different front bearing retainer. the early transmission cases used thrust washers, the later ones did not. The tops are different, as the left brake cars did not have provision for the brake handle. The later ones had the handle in front of the shift lever, the latests one had the handle on the side. The rear bearing retainer has the spacing of the holes for the bolts that hold the U joint housing together, the later ones had equal spacing.
There are probably other differences, but that is what comes to mind just now.