This overhead cam engine was built in very limited numbers for racing. Without superchargers, which were banned in 1949, the bikes were not particularly successful in the 500cc solo class (although Walter Zeller got 2nd in 1956 behind John Surtees on an MV-4 in the world championships). BMW won almost all of the first ten places in the world championships in the sidecar class from 1959 to 1972. The front suspension is called an Earles fork, invented in England. You will see a similar suspension on the R69S.