Two versions of the rear pinion
	At serial number 325,000 the rear end was beefed up. On the bottom pinion - from a later tractor - you can see that the teeth are longer than on the top one, which came from an earlier model. The crown wheels on the later tractors have correspondingly longer teeth which yields a larger overall diameter. The final drive ratio is the same either way, at 40/6. The rearmost bearing came apart when I removed the top pinion from the tractor and the inner part of it is still attached, which is why it appears to be a different diameter. On the early ones the rearmost bearing is held on with a circlip whereas the later ones are pressed on. Despite the differences in the length of the pinions, diameter of the crown wheels, and heavier rear axles, the entire rear section of a later tractor will mate up to the rear of the gearbox of an earlier tractor. I believe the earlier crown and pinions are no longer available.