These magnesium wheels were made inhouse by Schnitzer.
As far as I know they existed in the following sizes :
10&11 x15" (1970-71 race cars with +7,5cm flares)
11&12 x15" (1972-74 race cars with +10cm flares)
Sets in 9&10 x15" may have existed for road cars with flares, I am not 100% sure...