[dsraven]

the inspection holes for checking the lining thickness are usually around the 10 and 2 position if the wheel cylinder were to be at the 12 or 6 position. if you have no holes and are not sure if you should drill them them remove the drum and see where the spot is before you drill the holes out. this is so you dont accidently drill the hole where the shoes contact location is. wouldn't wanna mix that up.
there is always the google images where you can check a new backing plate that would show the inspection hole locations