Hello everyone. I'm new to QB, but have already found a wealth of helpful information while searching prior posts and threads - I'm so glad I found this group! I recently purchased a 1923 Model 66 Red Eye treadle machine that I am restoring for my own use. Luckily, it was in pretty decent shape, all parts moving fairly easily as they should, so I mainly just need to give it a good clean, and replace a few missing bits such as the slide cover and the belt.
But in doing research here and elsewhere, I've come across references to Model 66-1, 66-3, 66-4 and 66-16. ISMACS lists this as a model 66, but that is all the information I have. Could someone tell me how to tell which sub-class of the 66 I have or what the difference is between the different sub-classes (i.e., difference between a 66-3 and a 66-4 or a 66-16)?
(I tried to upload a photo but kept getting an "
Upload of file failed." message 
Not sure why - the pic is under 5MB)
Many thanks, in advance, for any insight you can provide!
Kelly