Lesco sells brackets for mounting their spreaders on the trucks. They even sell one that mounts into the receiver hitch. You have to specify which type of spreader you have. there is a height difference between the 4:1(old style)vs the 5:1(new sealed gearbox). All units are made with stainless steel. Westheffer Supply also sells different types of mounting systems
Anthony - That will probally have to be custom fabbed. An idea to keep in mind. Make it so that you don't have to take the ride on unit off to get to the push spreader. You don't want to have to take the time to unload the ride on unit every time you use the walk unit.
I don't know why PermaGreen didn't make a rack that would also hold a push spreader. While their unit is nice, it is not a 100% replacement for a push unit.