I agree about epoxying up the holes. Those backs are Nylon, and the epoxy will be easy to remove if you ever need to.
Also, beware, some C*x engines made in the late '80s (before I went back and fixed the problem!) had larger openings in the backplate than the venturi. Bad, bad news for good fuel draw. The venturi should be the same size or larger than the hole in the backplate.
Also on old backplates, check the screen, if it still has one. They can be really blocked up with old, congealed castor oil. I just remove the screen and smooth the inlet to remove the screen retention ridge.