OK, I can finally add to this thread. I am doing the conversion to c7 hubs on my rear right now, and I think I have a generation of upright not shown in this thread yet. See pics bellow. Sorry for not rotating them, posting from my phone.
What I have looks like the flat upright with an pocket engraved in it for the raised perch the bearing sits on. This perch is removable and looks a hell of alot like the adaptor I was going to make. Bolt pattern is of coruse just off for the c7 hub, but I can make a one or two piece adaptor that sits right in that pocket, has the right diameter for the c7 hub, and clock the bearing 90 degrees.
Has anyone seen this before, or am I just blind.