That actually is the correct mag collar for the solid-frame 97, only the takedown model used the other design. The solid-frame model is subtantially less common, but they were made at least into the 20s. All the WW1 era Trench Guns were built on solid-frame receivers, but the WW2 era guns were done with the takedown receiver, in spite of the fact that the heat shield interferes with the takedown mechanism.
The 93 does use the same mag collar as the solid-frame 97, but is identified by the shorter receiver and the ejection port coming up higher and having a thumb cut-out for single-loading. Detailed pictures can be seen here:
http://www.antiquearmsinc.com/winchester-1893-shotgun
I susect that alot of the guns that have been identified as 1893s on this site will actually turn out to be solid-frame 97s.