A reply to Gus:
Thanks for you response. I'm familiar w/ the rear mounting bracket that Blum sells and I have those. I suppose that my main problem is the side to side alignment. I have thought of making a jig from some staight plywood. Not sure if what I have in mind will work until I actually make it and try it out. I do not have the luxury of access to the insides of the cabinet from the top. Counter tops are in place as I am trying to upgrade our kitchen by making new doors and drawers with modern slides and hinges. The doors are a snap, however, the drawers demand a bit more accuracy. I confess to be new at woodworking, but I'm learning fast. I will try to get some photos posted in a couple of days. Your idea of a block of plywood used to help locate the rear bracket is helpful. I'll try that one. I'm still unsure of how to solve the side to side alignment, but I have an idea for a jig. Remember, these are existing cabinets of 1970's vintage construction.
Thanks for your advice.