Your timing on this is about 3 days late! The footrest is almost identical with the rear footrests on the Healey which I completed restoration of two days ago! The only significant difference is that your footrest is tapered along its length in a manner guaranteed to make the footrest rubbers work their way off to freedom. The Healey footrests have the same U - section as yours has at its inner end throughout their length. At the outer end, the metal is turned outwards for about 1/16" on all 3 sides, presumably to keep the footrest rubber in place. Replacement rubbers are a standard item for Jeff Hunter (for the Healey type ones). The system for preventing the footrest falling down whilst travelling without a pillion passenger is sheer crap in comparison with the Ariel system. The pivot bolt has a shakeproof washer beneath both the bolt head and the nut. So you tighten the nut until there is enough friction between the two parts for the footrest to stay upright. The shakeproof washers maintain this level of friction (in theory, but probably long enough to last for the warranty period). Then you need to tighten the nut, only to find that the shakeproof washers no longer resist shake!
Given the undoubted improvement of the assembly with the modification to keep the rubber on, I suspect that this is an inferior make item rather than an aftermarket one. The fact that Jeff Hunter has the rubbers as standard items backs this theory up. BSA or Triumph are the favourite culprits. When building the Healeys, Tim sourced parts from whatever was readily available. Hence BSA instruments and stand, BMW handlebar switches, Ducati wheels, Honda indicators and main switches, Ariel engines, gearboxes and handlebars, etc.
I really don't fancy trying to remove a footrest rubber to take a photo for you as I think it would be less than easy, given the experience of fitting them.
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.