So you used a go-kart diff on the back end? Sweet!
Are you using a homebrew servoset for the steering?
If you have an automotive sponsor (GM, Ford,...) you should see if they can give you a graphic for "Electic Power Steering" or make one yourself.
Are you going for autonomous? I guess your putting an encoder at the tire since you won't be able to figure out (easily) from the shifter how far you've gone?
-q