I have both of these engines and they are great
http://www2.towerhobbies.com/cgi-bin...?&I=LXPV47&P=7
http://www2.towerhobbies.com/cgi-bin...?&I=LXBHL3&P=7
You can get the secong one with a rotary carb if you prefer.
Regardless, I would get a .15 instead of a .12 for a 4 wheel drive vehicle.
Have fun!!