I also started to think about my parallelogram rear brake hanger. The existing brake hanger is secured to the swinging arm by compression via tightening of the wheel spindle and a slotted lug which allows for rear wheel adjustment on the inside of the swinging arm. as can be seen from the picture the caliper holder has a crank on it of 10mm.
I plan to make a floating caliper with 10mm plate and 75mm aluminium bar. I do not think I can bend 10mm plate accurately (twice) so I plan to make the caliper mounting plate flat. I will spacer the disc out by 10mm. Probably cutting it from one piece of plate rather than 6 x 10 mm spacers. The caliper itself will be mounted above the wheel spindle and the mounting plate will extend below the wheel spindle where it will be attached to a spherical bearing and a reaction rod to the back of the engine. The 75mm bar starting from the inboard end will be 55mm for 10 mm then 75mm for 10 mm then 55 mm for the remainder of its length. The bar will be bored to take the wheel spindle and machined either side to take 2 x standard rear wheel bearings. I think that will work - all I need now is the drive belt to be delivered for my lathe.
img