I have two non first syncro Moss boxes from MkV11s, one box OSH, has the cluster countershaft as a complete unit while the second box JLN the cluster gear has the individual gears assembled on a splined countershaft.
The OSH box does not have the stop pin on the first gear hub & the case hardening on one tooth of first gear is badly worn.
Can I replace this hub & first speed gear with the hub & first speed gear from the JLN box where the first gear hub has the stop pin & the case hardening on the first speed gear is reasonable?
Both gears have the same number of teeth & look similar although there is a slight difference in the width of the top of the first speed gear teeth.
Comparing part numbers from the Mark VII parts catalogue:
SH and SL 1st speed gear wheel C1897
2nd synchro sleeve C1853 (wo/stop pin) superceded to C7479 (w/stop pin)
JH and JL 1st speed gear wheel C2040
2nd synchro sleeve C2679 (wo/stop pin) superceded to C7480 (w/stop pin)
If they had been the same part numbers, I would have said, yes they are the same.
Since they are different, I am inclined to say, you need to measure carefully and figure out what are the differences.
Gearboxes are close tolerance assemblies. The SH and SL were made by Moss, where the JH and JL were made by Jaguar, so one can’t just throw random parts together and hope it works.
There had to be a reason the part numbers are consecutive from the Moss-made box to the Jaguar-made box. It may be dimensional differences, it may be tolerances, it may be for record keeping, or warranty claims.
I presume you have a 120 and need the SH tailcase because the JLN overdrive won’t fit in a 120. You could also look into swapping the SH mainshaft and tailcase onto the JLN. But there again, the SH mainshaft is C4106 and the JH mainshaft is C4107 so there is some sort of difference.
Let us know what you find. I think this is the first time this question has come up on this forum.