Kevin,
All good advice so far.
If you are breaking off the nubs then you've got a real problem. But take heart. Make sure you're e trying to turn the nubs in the right direction. When looking at the end of the wheel cylinder (not seen because of the drum) remember the proper direction. Counter clockwise is the direction you want the nubs to turn to release the shoes.
Take a two screwdrivers and reach behind the drum at 180 degrees apart and keep working back and forth with pressure against the drum. Eventually you will work it off. Also, release the brake bleed screw. You're going to need to clean the cylinders up anyway and will need to bleed them upon reinstallation.
If all trials fail, take a big sledge hammer a bust the drums. They are cast and will break. Problem solved. Spare drums and hubs are a dime a dozen.
Good luck,
Charlie
BTW: Don't get impatient. And, don't worry about messing up the internal parts with the screw drivers. You ain't gonna hurt nothing.