I don't seem to recall any manual-adjust brakes with the adjusting slot in the drum instead of the backing plate. It's possible someone might have taken a giant leap backwards and retro-fitted your brakes from self-adjusters back to manual. I don't think it's going to be possible to get a good adjustment without the wheel mounted to get a feel for when the shoes are adjusted to that "firm drag" point I mentioned. At some time in the future, think about going to the later system with the self adjusters- - - -it's a lot less work in the long run to let the brakes take up their own slack.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!