We will be working on the museum set at some point over the summer and I will gather more information.
Meanwhile, perseverance pays off. It took me a few tries to get there but I finally found a 4 pin tube socket that fits in the RR-359! I will need to slightly enlarge the mounting tab holes, but the phenolic body fits perfectly.
It is an Amphenol SK4P from RF Parts.
https://www.rfparts.com/sk4p.html
I recommend perusing their offerings if you are not familiar with the site. They lean towards transmitters and have some interesting vintage parts.
It's in the foreground here. Body and mounting collar are smaller than the industry standard.
Obviously, it's not the same as the original, but will get the job done.
