I've got an original Hengstler with metal connection box and have been thinking on this a little over this last day or so in readiness for my own build. And think I may have a relatively simple solution to this without the need for drilling etc.
On the metal connection box there are two square holes cut out of the side one showing the eagle the other simply shows the inners of the Hengstler and its this which I think is key.
My solution would probably buck a trend, but here goes. If you consider the 4th photo above posted by 'Vern: TK Bondservnt 2392' you'll note that the bracket is set so it hangs from the rail. Why not simply invert this so it goes upward, thus hanging the hengsler from the inner square like a hook, I reason that a really snug fit would probably hold it in place pretty well, and could be enhanced with being slightly wider with a groove cut in each side. By inserting the hanger into the hengslter at an angle and turning it to lock into place it would stop it sliding etc?
Has anyone considered this or tried it?