Either print the plate or laser cut two of it.
Print the motor brackets, tap threads into the holes
Either print the spacers or use M3 nylon standoffs. 30mm should give clearance enough for a 18650 battery pack in the lower deck.
Use 16 M3x6mm bolts.
The wheels are made for 40mm sewage piping o-rings
Stick everything else to it and there you go, you have a robotic platform for those nice N20 motors! There's space for an Arduino Uno with a h-bridge shield on the top and you can strap an ultrassonic sensor on the front, or headlights or whatever really.
Here's where to get them:
The only part that needs to be custom made are the plates, for everything else there's a readymade component out on Aliexpress in case you need a hundred copies of this. The brackets don't even have to be used, since the holes allow for a pair of nylon straps to be used as well.
Alter the plates and the drillings to your liking.
Suggestion: print a pair, add a laser diode and a laser detector to each one of them and make robot laser tag.