Info on 7.25 to 8.75 backing plate swap

The small bolt pattern axles use their own backing plate, as it sounds like you've already discovered. I'm unaware of any other options except possibly a disc swap of some sort. I can point you to a couple of vendors if interested in discs, but if you want to stick with small bolt pattern and drums, the stock setup is about all I'm aware of.

If you decide to swap in some big-bolt axles, you will have more choices, including the 11" setup you already have.