When I first noticed them stuck, they were only dragging. It was possible for two people to push the car. I disconnected the cables and with the help of a friend, pushed the car back and forth to try and free them. No joy. Unfortunately in the intervening time since then, they have become too stuck to push. I hired a tow truck to move the car to my new house, and he had to literally drag it out with a winch. No lawnmower I have access to is going to free them up! I'm in the process of moving, and may not get to it for a week or two. But I'll have another look at the drums to see if I can execute the process in the FSM. The key will be seeing if I can apply enough torque to rotate the drums into position.
BTW, this seems like a good time to give a shout out to @Patcon, who came to my new house that cold, dark night to help me push the car into my garage. Not only were the rear wheels locked, but we couldn't get the ignition key to free the column lock (this car hates me). He was able to remove the column lock through an elaborate, technical process I've been sworn to keep secret under penalty of death. Even so, it took wheel dollies, a jack, and a tow strap using both our trucks. But we got it in! Thanks man!