I think the back-clamping 66-1 is from 1915. I have since found all of the little doo-dads that originally came in the fitted drawer.
The 3/4 size 28 treadle from around 1918 is very cute and I found a hemstitcher attachment for it - but I haven't used it except to play with. It has a complete set of doo-dads, too. I always like to make sure that my "gals" have their "stuff."
The 27 is from 1898, if I remember correctly - it is much more beautiful now, after a complete refurbishing. Sews like a champ.