A real head scratcher !!

[Chamberpains]

Sure looks like your s-cam is shot... I can't tell if it's the top or the bottom roller is worn in to the s-cam more than the other. Are your shoes mounted on the anchor pins straight? Having the s-cam worn out like this won't let you back the rollers off as far as you have them. It's probably at this point backed off to far. Try cranking it forward a little and see if that allows you to slide the drum on.

If I remember correctly those Eaton brake drums were a tight fit. So if there was any mis alignment the drum was a pain to get on.