John,
Go back to my post on the first page of this thread and look at the way that we are locating the axle, skip all of the monkey motion that we went through to get the shocks inside the body. The axle is located by three arms, the lower ones, that also link the shocks to the axle and the middle one that is located approx 7 inches above the lowers and provides lateral location and also front to back location. It also provides the means to set the axle caster. Our axle is 44 inches between king pins and the front of our car is pretty lite, approx 400 lbs. All of this is located inside a tank that is around 13-15 inches in diameter at the axle area. We have ran this last year at the SCTA meet and even with the rough course we had no handling problems related to the front axle, that we know of at least. If you do go with a four bar or hair pin radius rods I would highly suggest using a three bar set up as it will prevent the inherent binding of a four bar or hair pin set up as they try to twist the axle in situations in which one wheel is raised above the other.
I agree with our aero guy to go with a round section design, much more work but much better aerodynamics. Flat bottom cars are so much more easy to build but not optimum for aero.
Rex