Hmmmm. I did find the screws as you mentioned on the bottom and sides of the 'railrider'. The upper roller may well be seized as I didn't check to see if it moved freely. It works smoothly with the Cambo rail.
I'll take another look. It was a really tight fit and it might be the extruded aluminum is nominally 1" but enough oversized not do work.
I may also have a line ('the bay') on a Cambo short rail if all else fails (or one will turn up sooner or later). I originally bought a 48" piece of the 2040 (or whatever it's called) extruded aluminum to make a 34-36" rail and use the extra for a short rail. That plan foundered when I discovered I couldn't get the standards to go on so it's worth another try.
Thanks for your help!