[Jac Mac]

If its grinding going into reverse then your clutch doesnt seem to be releasing completely, I would work on that before rebuilding the trans for no good reason.
Small steel tag between top/bottom bolts on RH of main case should be a start for ID.
Is the 'new' clutch M/Cyl the same bore as the old one, this might explain if problem has only started since replacement.

Jac Mac