[KensRedZed]

Interesting idea Graham. Thank you very kindly for the suggestion. 

I can drill a 3/32" hole straight though an aluminum block and install it on an axle in the chassis. One 2mm hole 90 degrees parallel on one side, and a 1.5mm on the other. An inline jig for any motor. Epoxy will fill any gap. No brass spacer required.

Trouble is, how do install the pinion after the motor is glued in? The pinion goes to the end of the drive shaft when I install a motor. There is nothing extending past the pinion once it's installed. I don't use the slot in the crown to keep the axle in place. Chris Walker will be the first to say "using the slot in the crown to keep the axle in place translates to a loss of power". Words of wisdom. It's wise to listen to someone that builds winning cars.

Maybe I can use the jig to make it easier and more precise to figure out the right brass spacer, and it's position relative to the motor?

My brain is thinking on how to use this new information... I need to sit down and go through the physics.