Thanks for the info Denis.
How worn was your driven gear after 6 months of 'incorrect' use (before you changed the driving gear)?
I may just do the same (whack it in and see how it goes).
Sounds like changing the gear in the tranny is not going to be fun. I do have a bit of input shaft noise in the W57 - maybe it is time to get it ripped out & reconditioned & do the gear at the same time.