removing the brake drums from my Power Wagon

Use a flat screwdriver from the backside of the plate adjustment hole and back the shoes way off out, and if they still won't move try opening the bleeder valve on each wheel and maybe the shoes will 'relax' enough to allow you to get them off. If it's not the shoes binding it, copious amounts of WD 40 or light machine oil overnight soak may help. There is really nothing to bind it on like that except the shoes

like David said, those shoes must clear the drum so make sure they are backed off all the way- on old Power Wagon just might have some corrosion issues- you may have to blast those puppies off- or, less fun, use an impact puller (slide hammer)

Blasting sounds fun.

Yah something that old there is always issues. I'm thinking that they were wearing uneven accross the shoe/drum. Some peaks and valley's to ruin your day. Try the above. Before you pull hard or pry try turning and tapping the drum with a hammer. If it is really bad you may have to cut the shoe holder pins from the back so that the shoes can "pivot" off of the brake cylinder without damaging it. Something that old you should get a hardware kit anyway.