I acquired my Foot Stirrup in the early 1980s.
My Foot Stirrup is 129 mm. long, 166 mm. wide, 42 mm. high, and weighs 246 g. The stirrup itself is made of two 1/4-in (6.5 mm.) steel rods bent to shape and welded to form a closed curve. The top rod passes through a milled steel cam mounting block, and the ends of the lower rod are arranged to keep the block from sliding (it is free to rotate). The block has a groove for mounting the cam. A plastic bushing fits in the cam eye, and then the cam is bolted to the mount.
This is a noncommercial device with no markings.
In the late 1970's I placed a challenge in The Nylon Highway #7 for someone to design a method of mounting a foot Gibbs that met a number of probably contradictory and unachievable criteria. A few years later someone - and I've lost my record who - gave me this foot stirrup to evaluate.
Depending on the boots being worn, the stirrup is either uncomfortable or not noticeable, so stiff-soled boots are to be preferred. I find that the mount tends to rotate, so a bungee should be used to keep an upward pull on the Gibbs. Some form of chicken loop should be added as well, since the boot tends to come out of the stirrup.