As I recall, that is a holddown of some sort. It keeps the shoes from slipping off the "top anchor pin" (that one I DO remember!)
If you've got a sample part, you can use those dims to figure out a replacement. I've made them out of iron washers before - get one that fits the anchor pin, and grind the sides down to fit under the drum. It's not a structural part, and there isn't a lot of load on it, so you can get away with a bit. Hell, the OEMR ones are mild steel anyhow (probably something like 1018 or 1020.)
5-90