Parts are available. I don't think it was ever imported directly by mb but there are some around. The tranny is notoriously noisy when in neutral, that said if it sounds like something is tearing itself to bits there may be a problem.

I've had a couple of these rare 5 speeds and they are lovely.

Greazzer has three now I think, one which I used to own.

Good luck on your swap Beware of the flywheel issue. Search for 617 manual conversions and flywheel threads there are several.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.