I have helped with a couple of TT31,s and TT21’s. The TT31 is very good, the TT21 is quite fiddly and needs to be positioned closer to the pilot. If you are replacing a KT76a then the TT31 is a true slide in and forget solution, others not so much. The TRT 800A is the other option but that is harder to fit.
Are you going to keep the existing encoders?
Rod1