You'll have to do a smoke test with the engine running... See if there's a difference with how the air is drawn in!! The corvair engine uses a fan with straight blades, no angle or curve to the blades at all!!
I suspect Top banana was on the right track and it was there for easy fitting of the pump, the cap fitted instead if no pump. As I haven't got the funky cap anyway I'll stick with the one that's cleaned up already.
