Casting number on the seat is 361A. Thanks!
I don't have one to look at anymore - I want to say a piece of 5/8" cold rolled could be formed to make the rail, it was held to the seat with a nut above and one below on the seat. Backrest if memory serves had a bolt on back of the rail that went through the support for seat back, there was a spring between the seat support and the nut on the end of that bolt. Should not be difficult to fabricate other than the bends in the cold rolled. Just be careful not to break the ears on the cast iron seat. -- cts
"Sandman" used to make them. I do not know if he follows this website anymore. I can post a photo of something to give you an idea.
I bought a set from him and wish I had bought a second set now
"Sandman" used to make them. I do not know if he follows this website anymore. I can post a photo of something to give you an idea.
Thank you for the lead. I PM'd him yesterday. It doesn't appear he has posted in a couple of years so we'll see how it goes. Fingers crossed.
Photo of one in case you wish to make your own.
Another angle.