I have recently up-dated my Dana 60 web page and there may be some useful information for you there. Narrowing of a front D60 is described in detail. The rear is simila,r but easier since you dont have to deal with the knuckles. I also include some info on the rate 35-spline rear units.
http://darkwing.uoregon.edu/~jrice/cruiser/D60HD/D60.html
http://darkwing.uoregon.edu/~jrice/cruiser/D60HD/D60.html