The Morgan rear drums on your model will have the self adjustors. This makes backing off the shoes a bit more tricky than the manual version.
As above it would be worthwhile to establish where the problem is coming from. My bet would be seized wheel cylinders, but the handbrake cable is also a possibility.
If the cable is OK, you are going to have to get access to the inside of the drum in order to make more progress. If pushing the car is not possible then getting the shoes to release off the drums is going to be a tough one.
First release the 2 small bolts which locate the drum on the hub.
Tapping with wood on the outside of the drum in different places may work , but if driving it at low speeds doesn't, I have my doubts whether this will either.
If push comes to shove , you might need to pull off the drums using a fair bit of force , please do make sure the car is secure before doing so, and have a helper nearby. Once off, you can back off the adjustors to their minimum, and set about removing the shoes and springs from the cylinders. You might notice if the pistons are extended from their housing. It may be possible to tap them back in again (gently with a wooden drift) and then work them in and out without getting a fluid leak , but I would have a couple of wheel cylinder repair kits ( or wheel cylinders if the repair kits are not available in Oz) available "just in case"
Once you have dealt with the cylinders I am guessing that the drum will need a clean up on the friction surface at the very least. I would then clean everything up nicely so that the cylinders slide in the backplate and the adjustor is operating freely. Then re-assemble everything (much easier with 3 hands than 2) , set the adjustor , and tap the drum back on again. It should rotate relatively freely when the shoes are not in contact , and if this is not the case remove the drum (this time it should be much easier) and reset the adjustor slightly.
Others here may have something to add which has worked for them.
Good luck
