They actually came with Briggs motors ?
Indeed they did, Clintons too. I don't think Tecumseh was the standard engine until sometime in 1967 which is when you can see the change in literature. Early '67 adds/photos still show the bike like is listed *which those photos would have been taken in '66, and Lit/adds by Christmas of that year show the models that most people are used to seeing with mainly Tec's and Hodaka.
This is the late '66 bikes from an early '67 catalog
this is Christmas 1967, Main change to note when compared to above is swingarm design/update. and not a perfect shot but can tell the badge was now the Western style font lettering etc..