Schneider make the 28 mm PC-Super-Angulon in Nikon mount - the fully manual mount is easy to change and, in addition to the mounts listed by Schneider, there's also a mount available directly from Leica. B+W make a special filter holder (for unmounted 74 mm filters) and hood for it. It's a very nice lens whether shifted or used as a normal 28 mm lens. I use mine on my R6.2 and on my FTn/FE2.

Best,
Helen