I once operated a GE 45-tonner that had originally been equipped with 14EL air brake equipment, but at some point had been modified. The 14EL stuff was gone, replaced by an SA2 operating valve. It worked just fine to stop the locomotive, and if it was connected by the usual method to cars, it would apply the brakes to the cars. I never really poked around under the floor to see what had been done with the distributing valve or even if it was still there, but the system seemed to work okay as long as you didn't try to put a big slug of brakes on all at once unless you needed to make a fast stop.