Someday, I hope to acquire a Hammond (Multiplex or Folding), and a Varityper (one of the proportional spacing models, before photo-typesetting). In the meantime, I'm trying to learn as much about them as possible, ... and not finding much information. 

Does anyone have recommendations for information on these machines and companies? Books, or websites. I've looked through hammondtypewriter.com, Richard Polt and Robert Messenger's sites, Robert & Weil's book, and though there is some good information in these sources, I'm still looking for more. (I have yet to read through Hammond's patents or Etc. back issues).

Some questions I have:

- Model information: How to identify and what are the capabilities of the various models? E.g. when was proportional spacing introduced? When was full justification?

- Technical information: It looks like most Hammonds or Varityper's require a bit of work to get fully operational (I want to type on them, not just look at them), so I'm looking for any information that would help in that regard - service manuals, parts diagrams, tips, etc. Also any information on how they work - though I suspect I'll learn this mostly from taking them apart and putting them together again (which I'm really looking forward to). 

- Rubber vs Aluminum shuttles: I've seen some places say they're ever so slightly different sized, thus not both usable on the same machine (without some jiggering), and others that say that they are perfectly compatible. Which is correct?

Thanks!