[Jeffhs]

I would think you could use the same yoke with either tube, as RCA and Zenith CRTs are basically identical except, of course, for the brand name.

As to the issue you mentioned with the size difference between the neck of the Zenith tube and that of the RCA: I don't think it makes much difference, to tell you the honest truth. I have read posts on this forum from people who have successfully replaced Zenith CRTs with the much more reliable RCA tubes, so obviously it can be done.