I used to have a house built in the 1880s, with non-standard sized doors. Some jerk smashed the (non-rectangular, probably-hard-to-replace) window of one of them on Halloween one year, so we got a used door of similar size from a shop that was sort of halfway between ReHouse and an antique store. (They sold used house parts, but usually older and/or higher quality, and also old furniture and cabinets.)
I measured the width and height of the door, and bought a new door based on that. I think I remember my husband cutting new slots and drilling new holes for the hinges - the old cutouts were still there, but not visible while the door was closed. That, and hanging the door, went fine.
Installing the lock was a nightmare, though. I hadn't measured the
thickness of the door, and the new door was a little thicker than the old one, so it wasn't flush with the wall when it closed. The old door had
a lock sort of like this, so we figured we could buy a duplicate and replace just the door half of the lock, leaving the wall half in place. Nope. The door is sticking out further, so now it's misaligned and everything is terrible. We did finally get it working somehow, but I don't remember how.