Nello, nice job ! But the obvious drawback is that you must change the gearing with the spur which is more than a PITA ! I did the same as you on my own car but later I switched to the CR2 sloution with the extra idler just at the bottom of the motor plate instead of on one motorscrew, much better that way ! You'll have to re-drill an elongated hole for the bottom motor screw though, but that's no biggie.
If you manage to attach the idler axle with an excentric hole you wil even be able to adjust the idler-to-spur mesh, apart from the pinion-to-idler mesh, really the best solution to avoid mashed gears aka " teeth salad"
. This way you don't rely too much on the precision of your drilling. ; -)