[BBray_T1296]

Are you asking how to hold the crown gears in the module in place? or the spur gears between the motors.

When we did our car/crab drive in lunacy and breakaway we used one single brass pillow block to hold both crown gears and support the axles. of course, it looks like the large crown gear shares an axle with the wheel here, where ours had another stage lower down

For the spur gears (depending on live/dead axle) there is hardly any axial load (gravity isn't much) if you can machine groves for E-clips they would work just fine. Shaft collars (especially the thin and light VexPro ones) would work as well

EDIT: looking back at the pictures, PVC or Delrin (or anything really) spacers would hold the spur gears