Here is a fork leg that has been done. Its yet to be tested as the bike is wip.
My mate who is a plastics engineer, cut of the tangs and welded them back on the other side. I suspect BMW only make one type of leg and cut the unused side off.
Have also swapped out the pre 81 internals for later 'Brembo" leg ones.Since then have decided to go for Racetech Emulators so could have used the original internals as you just drill the damper rod holes out.
The later internals drop in and you only have to drill out the base fitting.
As for the brakes themselves, going to use a Ducati 'coffin lid' 13 mm master cylinder and braided hoses. Should make the ATEs work quite well. I want to retain the early disc look for the bike which is only going to be used on the track.
I looked at using the Brembos but they don't clear the spokes of the wheel as its the wide hub not the narrow one used. The narrow one looks to be a wide one machined down as the hubs are in two halfs.
Hope the pic helps. You can cut and fab up the tang yourself, just need it welded. I could spend a bit more time on it and you'd never know...