I have done several SH's and SC's, successfully.
New balls are readily available and oversize are not, nor necessary.
I disassemble and bead blast the drum and expansion plates. install new pads, springs and balls. Reassemble dry,adjust, and see how it works.
This assumes that the plates, drum, and bull pinion carrier surfaces aren't scored too badly. If they are scored have them machined.
If it won't adjust properly there is too much wear to the drum and expansion plate surfaces. These are the machined surfaces the pads contact.
The fix for that is to have your machinist remove material from the drum. The external part of the drum that meets the bull pinion carrier. That compensates for the internal wear.