My brother has the 57 Custom that our grandparents purchased new.

Came with the 223 6 cylinder and OD.  He has it redone with a nicely built street 390 but kept the original 3 Speed OD.

I know there are two versions of the OD and I would assume the one in a 6 would NOT be the heavier duty version.

That said, it's been fine for 63 years until this weekend.  Just cruising along at highway speeds and it kicked out - as if he'd pulled the lever.  Then an ugly grinding noise.  Transmission is working fine except no OD, of course.  Doesn't freewheel so combination of sound at end of function, and that factor, seems to rule out electrical issue.

So he's looking for either a semi-local shop familiar with these transmissions for a repair.  Or someone with one for sale.  Probably should go after the heavier duty version but I think he'd settle for a replacement for the one he has if available.  I think the beefier one can be quite a bit pricier but might be worth it in the end.

Located in Iowa near Davenport/Muscatine so Eastern Iowa or Western Illinois would be ideal.

TIA