John Martin wrote:
I've got an old Gravely tractor and several gearboxes for the rotary
plow and rototiller attachments. ...

Hey, me too. A couple of years ago I cleaned out my shed of a bunch of
Gravely stuff that "I might need". Parted out a tractor, or 2.
Whenever I put a wrench to one of those machines, I'm impressed. Built
to last and they do.

The pinion gears are machined steel, but the ring cears are cast iron
- with no machining of the gear teeth. ...

That I haven't seen. Every Gravely gear that I've seen had machined teeth.

Bob