Nice to meet you Sarge, I too raised a boy, he's 21 now.
I had him riding a bicycle to school early as well, hahaha, I had to get a special wavier from the principle as he was in 5th grade and you had to be at least a 7th grader to ride to school.
It is great to see you spending time and sharing projects with your boys because as you mentioned, schools simply can't teach any kid the things his dad knows and can. The sad part is so many dad's don't these days.
But back to the motorizing...
Bought the black&grey&argyle 2011 (Huffy) model today and hid it where I motorize them.
So you have built one or more already?
Just allow me to caution you about putting any motor on any Wally World $85 Huffy type cheap bike, especially for your kid to ride with a motor.
It's not a matter of IF the bike will fail, it's HOW SOON, what fails, and when it happens.
It is usually the back wheel first too, no fun when you are cruising full speed.
Maybe just surprise him with a new solid bike a few month before you motorize it?