Norman,
I think a universal design is a little difficult, but you look to have a very easy set-up to work with. I would do a variation of this:
View attachment 22433
This is a flat plate. The lower hole is the axle hole. The plate thickness here is the thickness of the E80 nut and the stock brake plate thickness together.
The hole directly above the axle hole is the brake anchor. I put a SS bolt through hear and used it to bolt the plate in place. The curve in the outline of the plate, above and to the right of the anchor is to clear the lower spring box mount.
The remaining two holes are the caliper mounting holes. They were close to the blade on this design, but on yours, it is such a big disc that you have plenty of room to the left. I would keep the caliper close just to minimize the weight of the plate.
Finally, I milled the back of the plate to get the calipers to align properly with the disc. I think I used an overly thick plate that put the calipers in the right place and milled the remainder of the plate to the E80 nut and brake plate thickness. You may want to try out a flat piece of aluminum to make a fitting to calculate the caliper mounting offset relative to where the E80 nut and brake plate thickness are located. I used 4130 steel for the plate itself. I probably could have used 2024 aluminum, but I was being conservative.
It looks to me like the caliper in the photo is in a good place for the plate right now. The spring box is a little further forward when mounted on the eccentric, so I would move the caliper a little further forward.
Thus, the plate is in a fixed position and a fixed thickness where it replaces the brake plate and nut. The thickness of the rest of the plate will have to move slightly in or out depending on what the calipers want.
David