Make sure you back off the brake adjusters, if you can. THe brake drums often have a ridge on the inside the the brake shoes hang up on this ridge and hold the drum on. If worse comes to worse you can break or cut the heads off the hold down pins that secure the brake shoes to the backing plate. Don't worry about getting new ones, they are pretty standard. The only thing that is hard to get is the drum itself, and it might be easier with a dually drum.
Finally if it really gets ugly, email me and I'll send you a picture of how I did it with an extremely bad job. I took a puller and modified it to work on the big drums.
