I asked on national preservation some years ago now, and nobody seemed to know what I was talking about
The railways here in Australia used an identical tool, and I can tell you they work a treat. I had some and gave them away, One well-known boilermaker here had a batch reverse engineered and made from memory- doesn't help I know, but if you do come across some I for one would be interested. I also asked in a US preservation forum, and the general consensus was that they used a different tool and these were only used in large construction shops. Most railways formed the head by "Merry go rounding" using a rotary snap attachment as they put it- there is a Youtube video but I can't remember the title.
Ian