It is also possible that the layshaft bearings are toast.
If the layshaft bearings are toast, the layshaft may be no good as well.
If the layshaft is no good, it may have damaged the mainshaft.
My point, it may be better to remove the gearbox, strip it down and evaluate all that is needed at that time. You have to strip it anyway to replace the rear roller bearing.
The roller bearings are easily obtainable and are standard NSK numbers.
The needle bearings for the layshaft are available, but a little harder to find.
Can't remember the bearing numbers off the top of my head, but will try to post them after looking them up if no one else does.
--
'86 745T, '72 144E, '70 145S, '68 220S, '60 544