10" backing plates???

If you use a large bolt pattern 10" drum it won't work with those backing plates, they are different. Get some large bolt pattern 10" drum plates from any other car, then just get the brake parts you need from the car you got the plates from. The brake parts are available at auto part stores yet. I believe the wheel cylinders are the same and so are the adjusters. The 10" spring hardware kit should also be the same. I tried the same thing you did with the backing plates and they rubbed on the brake drum. I had a set of 11" cop car brake assemblies from a 1985 Fury lying around so I used them instead. I also went with the Yukon axles. You can also get your brake drums redrilled for the larger pattern, I have never done it but I was told it can be done. Good luck, Keith.