If it was me doing the repair by first item would be to check the Chassis and if okay I would remove some of the flooring inside in front of the Door and I would Modernise it by adding a small amount of metal to suppor the floor and frame the door frame to install a much more modern door sort of like my back door at our old house, but this actually better to do on a
Boler as it is way more curved.
I know you think I have a screw loose But I just finished helping a fellow fix his log cabin that was built way back in the 1890's we had to remove all the old logs and re-install new logs to fit, hard work that.
Peter