Thanks for the replies, in the end it slid off, revealing the base plate with the patents and serial number....a little research suggests this dates from 1898-1900. I can make some shims easily enough to accommodate a 120 spool. The camera had a 116 spool in it which I can use as take-up spool....but the winder is broken. Any ideas how best to fix this? I do have access to a workshop but am not the best at making things...so something simple would be easiest. The camera is shabby but the shutter works, lens looks clear, aperture slider works. The red plastic is missing for the window but I have red a red gel I can put in there instead.
Please see the images attached for the serial no plate and the broken winder key.