Cool! That may very well be the case. I found several models in the Rider collection that I thought were close to what you had too, but none that were exact matches. So I kind of think the same as you, that your radio may be modified from how it was sold when it was new.I have a few old tube radios like that myself, where someone had obviously swapped parts out in the past. Not just replacing tubes, mind you, but actually substituting them for different types and rewiring. One had even swapped an entire chassis, and that may be the case for you. On one of my radios, I put everything back stock but the others, I just made them work as they were and enjoyed them.
Wayne