I have read here that the transmissions from the gas engined 123 cars will indeed fit a 616 or 617 diesel, but I have never personally tried it.

The transmission mating up will be only part of the problem. You will need shift linkage, the proper driveshaft mating and clutch pedal and hydraulics.

I personally would not convert one unless had the entire donor car setting next to the recipient. That way, I can get every little piece right down to the proper trim, to make it a nice conversion.

Good luck with the project and let us know how it comes out.

Have a great day,