The rules he posted says it has to be either RWD or 4WD.
Are the batteries going to be alkaline or NiMH?
No fun. I guess rwd will be easier to make the 4wd... With just 1 motor that is. Or use the tamiya worm box and split it off to 2 live axles with 1/4 elliptical springs for location. You can use the high lift springs and cut them in half. I can't imagine you want this to weigh much...