Mopzilla

Hey guys.. I've found I have little time to fly my 1/2A planes (quit for now) but I want something for around the yard, and it has to be NITRO. I've decided to use my Norvel .061 nitro engine for a micro-tank project to run around the nearby empty lot and in my yard. Size: distance between axles: 3.8". The frame measures 2.5" x 5", but can be extended to about 6". Engine: the distance from the backplate to the center of the 16t gear I put on is 2" flat. Width of engine is about 1.25" with the muffler.

I am trying to find the best and smallest solution for putting power down to the wheels. I have the means of making manual clutches:
=======is a shaft:
==| |== unengaged, and
==||== engaged.
I'd probably use one or my airplane foam wheels as one pad, because they are easily replaced, and a metal disc as the other pad.

Here are my options:

1. Use one clutch, be it a belt engagement, or pad engagement, or whatever, plus a differential and brakes on each side.
2. Use a direct drive from the engine to driveshaft, use worm gears on the ends of the driveshaft, but have a clutch in between each worm gear and the engine connection (so one clutch for each side)
3. Use a 3-wheel type system with two airplane wheels connected to the treads, and the engine "moves" between them to create full throttle. To turn, the engine moves back a lil and to the side so that it touches only one of the two airplane wheels, thus giving power only to one side. This may be hard to make because of the sliding engine, but it might take up the least space.

If there are any other options please let me know. So what's the easiest and smallest option here?
thanks.