I cant confirm all of this! BUT ...according to everyone I've asked....the big hollow driveshafts are 9 tooth drivers for the longer tracks.
The solid bar driveshaft is for the 136 and smaller tracks and are 8 tooth. However they are supposed to be interchangeable in the IQ chassis as long as you use the correct track/driver combo.
I'm in the middle of a 136 to 155 swap. And so far everything is fitting. Except the rear mounts, I have to make those.
