I tried some rear backing plates off a late model (1500?) that had wire wheels (my 59 BE(948) has steel wheels). I don't know if that had anything to do with it, but I had interference from the get go when trying to install the rear hubs. The backing plates look like the right ones, but maybe they are not. On my car, The hydraulic lines were going to have to be moved as well, so I dropped the project and never got as far as fitting the drums. I now have disc brakes up front with the original BE configuration in back. I also had my MC resleeved to 3/4" on the brake side (left it at 7/8 on the clutch side)and have had no problems stopping. The car stops quickly without excessive pedal pressure.
I still have the backing plates with the new brake shoes and new wheel cylinders to go with it if anyone wants to give it a go on their car. Maybe I was doing something backwards when I was messing with this. If so, perhaps they are still good for someone that wants to do the upgrade. PM me and we can work out a deal. I thought I'd keep them around for a future upgrade, but what I have on the car right now works pretty good.