I have a 77 Stepside with a 4 link in it and there is a couple others on this board with the same.
I am in the process of redoing the truck again, I am narrowing the rear end to fit a set of 15x12 rims, adding another drive shaft loop, adding a new set of coil over shocks and building a tall deck 505 with an F2 Procharger. Check out my photo link and flip through the Stepside picts.
Good luck onyour project
Dan