Are you sure they are potentiometers?
I recall an avionic guy calling these encoders, have a look at the RS website.
Trying to find the component maintenance manual for this would probably be a good starting point, are there no part numbers on the items themselves?
I'm on furlough at present but I'll have a look when I get back to work (hopefully) to see if I can find anything, I'm interested in doing something similar.