i have only narrowed a few rears, but when the housing and brackets are done, i use a 2" diameter ground bar with steel pucks. 2 of which are bolted to the gear center bearing location. these have a .0015 id clearance for the bar to pass through. then the other 2 at the axle bearing location. they have .001 id clearance for the bar, and .002 od clearance for the bearing bore. i chain the housing to a piece of 12" I beam that has a very thick web and flanges. i test the axle bearing pucks for a super easy "slide in" fit with the round bar installed. if they don't just "flick" in using just tiny finger motion, i heat the housing and use a bottle jack to apply pressure to move the tube in the desired direction. let the tube cool, then try the puck. repeat as necessary until i have the puck fit to my satisfaction. let cool over night, then try puck fitment again. if satisfactory, then assemble rear and install. never had any tire wear, or tracking issues, doing this way of insuring housing was straight.