For a reduction gear, all they need is something like a planetary gear system on the shaft. The "Depth" of that gear system is only about two inches or so, so it wouldn't add all that much length to the motor.
you should contact them and ask...I have contacted them my self and was told that their battery and bms is too complicated for diyers...but may be you should ask them if they are willing to sell only the motor and controller combo...I imagine if they receive enough individual inquiries they might be willing to sell to usDoes amp sell its transmission also as separate modules for Diy EV'ers?
That's the easy part to figure out. First, you supply a donor vehicle (minimum about $20k right now in a quick search). Next they remove the ice parts, which THEY KEEP (and presumably sell). That's probably $5k in parts or more. If they are buying in volume, the motors are probably no more expensive than the money they recoup for parts, so you are left with batteries, controllers, peripherals, and installation for $50k out of your pocket. Assuming they get a volume discount on batteries, too, they will make out well.I would like to know myself how they kept the price down under 50 thousand dollars.