[Jayce]

I checked on the 6AX5GT and you are right about that. Even my tube substitution manuals list it as a sub, but caution that the tube uses parallel filament circuits. Further research also ended that option as that tube draws over twice the current of the 6X5. I guess that is ok with larger transformers, but not Zeniths. Wish it would work as I have a used example (untested) and a brand new in the box 6AX5 from RCA.
I too have heard about the 6X5WGT, but don't currently have any in my personal stock. I have a used 6X5GT and an apparently new RCA 6X5GT. The one currently in the radio is a 6X5GT and I think a Sylvania. I am pondering that WX5 solid state swap as well, but would still try to find a 'safer' 6X5 while researching that. Might have to see what my friend has for new tubes left at his shop and see if I can at least get a 6X5WGT or two.