I read on here that it is possible to use a rack and pinion, but if it doesnt go up and down with the axle, it will be less than perfect, I imagine that it would pull the wheels in and out of straight, ie toe in/out. I don't know cuz I havent done it, as I am on the same quest as you. but an adjustable rod connecting the spindles as was done on any stock straight axle would work. I havent got it figured out either. Besides, why not weld some rack and pinion mounts on to the axle, and let some u joints in the steering go up and down with the whole thing?