The cost of re-drill will depend on whether the shop is set up to do this kind of work (has a template, or dividing head setup). The other is which axle you have. Car or truck?. Some need a hole filled to redrill to 4 3/4". I used to have sections of cold rolled bar stock that I filled the holes with.
Chevy drums won't fit the Ford rear housing. Backspacing and center hole are wrong. You will have to redrill the Ford drums also.