In some order, I suggest
Try to unstick the drum by towing the truck. Backwards and forwards.
Let the adjusters off if they move.
Remove the handbrake cable and tap the levers.
possibly loosen the bolts holding the slave cyl and let it drop in a bit?
Pound around the outside of the drum shere the shoes contact to pop them off. This will stir up asbestos dust so wear a mask.
If the drum rotates you will be able go turn and tap it off.
