Ken, I am using a Losi crawler as the base for my Ford Super Duty. It is the 1/18 mini crawler. It is 4x4 and the steering servo is mounted on the axle. I am going to try to get the frame together and get the suspension under it soon and you can see how I did mine, not that you have to do it the same, just some ideas.

http://173.201.47.108/showthread.php?t=1005