They should have self adjusters on them. My '65 c10 has self adjusters on the drum brakes. Ya get it as close as ya can to where you can put the drum back on it. Once you drive it, it should adjust to where it needs to be.
If there is no slot, there *might* be a piece of metal that 'punches' out. Remember to put a rubber plug in it, if you punch it out.
-W
