Mark -
That style debuted in about 1937, right around the time (a little later) than the "Bugeye" Imperial. For some reason known only to Birtman Electric and Kenmore/Sears, it was kept around for quite awhile. It started off as a polished metal model and eventually morphed into a painted metal model.
Somewhere I have research that I did years ago about the Kenmore vacuums, dating each one by year of debut. If/when I dig it out, I'll post a thread about this one. Thanks for the great scans of the manual.