I don't know if the ignitions have a different curve, but I ran a qt50 with a mj50 ignition and it was fine.
Mj50 ignition has a stator, cdi box, and the selector box (for start and run selection). I never found any documentation for it, but I figured out how to remove the key switch and use a 3-way switch instead. My blinker switch: left == start, right == run, center == wizard magic neither. (edited)