Pretty simply, I had originally built my goKart out of metal I bought at Home Depot. The way it worked was that it had one drive wheel (rear right when facing the back of the Kart) and one wheel with a drum brake (rear left).
The Kart was doing close to 30mph at half throttle, so it was scary. Instead it was converted to use a wooden (heavier) frame. Once the decision was made to convert it to a Half Track, the same decision was made to make it a full tank.
1) Removed the engine, rear axle and rear wheels
2) Measured and inserted a pair of 1.25" threaded rods, 36" long each
3) Cut a set of metal cylinders to fit the bore of 2 drive sprockets (from InterLox), which in turn fit the shafts of a pair of electric motors