GOTO Mark-X Motor Candidates

The Tele Vue System mount motor arrived yesterday, it's a new one from stock.  I found the mounting of this motor to the Mark-X non-trivial and I probably need a machinist to help me out.  At the same time, I will need to hack the crystal to accommodate the speed difference:

And meanwhile, a Cloudynights buddy reported that another simpler drive could also accommodate 126T without modification, and the mounting could be easier as well.

In that case, the calibration of speed might be the hardest part, I will need accurate polar alignment and then I can adjust the speed, maybe with the help of my Lu070M.  However, it could be hard to have very accurate alignment without a properly tracking motor?  An egg and chicken problem.

So, I'll need to see which way I should go.