Did you remove the flathead machine screws (3of them each side) on the rear drum?........... I removed my drums with some well place blows with a hammer

The drums could be stuck to the shoes after sitting for decades. Sometimes dragging the truck with another truck or tractor will break them free. I’ve also had one that was stuck in gear which needed to have its drive shaft disconnected from the differential to let it roll. If nothing else works a tow truck or rollback may be needed to get the truck to a place where you can find the cause and a solution. Stu