The 116 might LOOK much like a 123, but that's where the similarity stops. The cars are TOTALLY different.

There are a few euro cars in the country with manuals. Converting one will require MANY more parts and fabrication than you can imagine. The only way that I would do one is if I had a donor car of the same body series setting next to the recipient. It is much more involved than the pedal assembly and cobbling together a shifter.

Good luck,