Your 61 should be wired for
12V even if it's not currently being used. The battery box was attached to the outside front shell just below the window, it was a goofy sized battery and is still available. The wires should be inside the box. If you don't want/need
12v for your use, you could add a 12v power supply just to run the fan. The should be a 12v circuit somewhere you can tie onto, perhaps under the pantry or in a cabinet. This vintage only had one long daisy chained circuit with no fuse block so any point is a reasonable tie in.