The collins 51-j4 had a rotating drum frequency scale in the 50s, So I suspect that Zenith did not a patent on it for the Trans-Oceanic sets:
http://www.radioing.com/collins/rx04.html
I have a Hallicrafters transistor portable (WR-3000) which is about the same size as the T-O sets. It was likely made in about the same time period and indeed does have a rotating drum frequency scale.
jr
Add: Couldn't find a pix of the Hallicrafters WR-3000 on the web, so I took one. It is almost exactly the same size as the transistor T-Os but configured as a "horizontal" set.