[lincpimp]

Ok, I did a similar conversiopn to the old emaxx tranny using a revo slipper and mgt mod1 spur gears. Traxxas is using the same backing plate on the slipper that the revo uses, and I am sure that they have left a small (1mm) gap between it and the motor plate. The motor plate appears to be the same thickness as the stock plate in the old emaxx. Since the new emaxx spur mounts to the top of the slipper (like the revo spur) there is some spce between it and the motor plate (more than a std emaxx peg slipper )

I just did some mesurements on my old emaxx tranny with the revo slipper and spur. Looks like a 12-15mm long shaft (from the front plate of the motor) would be sufficient, as long as the pinion is oriented so that the setscrew is betwwen the gear and the motor plate. I can't imagine the hvmaxx motor having a shaft shorter than 12mm.

A feigao L can motor has a 15mm long shaft for comparison purposes.