Make sure the "pads" that are on backing plate aren't Grooved and holding shoes outward too much. Sometimes you can grind the groove some flatter, but if real bad, have to weld them up to fill and regrind or replace backing plate.
Seems someone else had same problem on AD truck here. Maybe materials aren't as plentiful anymore now that asbestos if outlawed and they only have a few choices for thickness.
Use to be in old shops, they had a brake show "arcing" machine to make shoes match the arc of drums. Used to O/S drums so shoe still hit on full surfaces. Maybe if you find an older brake shop they could grind your shoes down to fit your drums. Take the drums with you.
