I also used the cab and chassis dually axle and used two inch spacers on the rear wheels (thats what i had there at the time) 1 1/2 woulda been perfect...... tho i didnt like the way it looked with the two inch spacers at first but its kinda grown on me i'll see if i can dig up a pic or two and post them up.
But i was thinking it would be better to take the spacers off when we pulled it because it off sets the wheels inboard enough were the rear tires aren't running entirely in the same tracks as the fronts (kinda like the pro mods do just not as drastic :evil) giving the rear tires a bite into hard packed track instead of loose dirt.....Idk if im on the right track with my thinking but theres a pull coming up i can hopefully talk her into pulling at were I can test my theory..
Dunno mine had it in when I got the truck.
Would you mind measuring the rear center to center of the wheels and snagging a picture? I need an idea for as now i just have nothing to drive haha.