When it is all said and done;;;; if you find you need to move the rear caliper brake or just the fender mount to one side a bit...then you shouild be able to find what we used to call a drop brake adapter. It was intended to put short reach brakes on a long reach frame. It was a small block of aluminum or steel, albout 3/4" or so. On one side was a bolt to go through the brake bridge. On the other side and offset was a replacement pivot bolt. Should be findable or something that could be fabbed easy enough. I remember making them several times in the 1970-1980 timeframe. PM me if you need a drawing of one to work from.