I would get 11x2.5” backing plates. 11x2” drums, and even shoes, aren’t that easy to find all the time. And you already have all the hardware and drums.
Lemme check my stash, I may have an extra set of 11x2.5” backing plates. I have some used 11x2” drums too, but I don’t think I’ve got any of those that are in good enough shape to run.