The BMW OHC bikes are functioning machines. There are several designs that have been done on the 1955-69 twins and also the 1970 & up engines.
I saw and heard run the 70 & up versions some time ago in Germany. They seemed to be well thought out design modifications to the stock engine. Since those engines have the cam placed below the engine the design has some challenges. The pre-70 twin mod'd engines have plenty of room for the replacement geared shaft.