Well, you're in the right place.
With a little luck, and a few ordered parts, logically you should be able to get two of em running by stripping down the third, which is what I would do...take the two best and restore...and strip the third down for parts.
You can still get a lot of the parts for em, as I recall...and the forum folks will be happy to assist you in the technical aspects and problemsolving.
Above all listen to the old codger you found, those guys know stuff that's never made it into repair manuals, and are great fonts of information and history relative to stuff they work on, you can learn a lot.
As for a manual, check the links under Resources at this site and moped2.org - you should at least figure out where to look, if nothing else.