I am not sure why the question of which came first, the 911 engine or the B50 was not answered. The B50 was not produced before '71(?), developed from the B44 with lots of changes whereas the 911 was first introduced in '64 as a 2.0L which progressed to a 2.4L 84mm bore in '72. There is very little in common between the 911 and VW motors. The cam box on a 911 spans all three cylinders. Just the heads and cylinders are individual. The 911 head might fit the B50 cylinder but it was designed for forced cooling and would probably overheat with just free air flow.