Since you said that there's no screws holding it on, I'll take it that there's no rivets either. I'd suggest taking the bearings apart and removing the entire drum and hub as an assembly. Then you can deal with the drum removal off the truck. There's a chance that there's rust buildup behind the drum. You may have to hammer between the studs to get it loose. An Air hammer works well for this. But be warned, if too much force is used, the drum can be damaged. I'd olny suggest the air hammer if you pln on installing new drums. If you are going to have them machined, they can be turned with the hub in place.
