I had purchased two sets of track,s both were on complete snow blowers. One ran (125 dollars) the other one was disassembled (65 dollars,) but the tracks were in good shape and complete.
I'm using two 350 watt motors from wheel chairs as they already have built in gear reduction.
Here is what a motor gearbox looks like inside with all the grease cleaned out.
The spring on the larger shaft was for the lever to disengage the gear by sliding it over on the shaft so the wheels can rotate freely.
I have removed the lever and the decided to not use the cover also as it will reduce the overall height of the motor/gearbox for more ground clearance. My new aluminum chassis uses a single aluminum plate the mount for the motors so that serves as the gearbox cover also.
Future plans include some type of two speed gearbox the the base can really move but I am still doing the CAD work and researching the gears as I would like to get it to fit into the existing gearbox.
My first chassis design was from mild steel because I could cut and weld it easily, and it was my first frame and I wasn't quite sure how I wanted it. The two 17 Ah, 12v batteries were mounted in the middle because my first thought was to keep the base a narrow as possible but as you can see in the next picture that did not provide alot of ground clearance.
In this picture the flat aluminum plate that ties the two motors together also serves
as the cover for the gearboxes. The stock cover was about 3/4" thick and had the manual lever sticking out of it.