I've got a pair of Japanese SU HS4's (38mm/1.5") made by Hitachi (made for old Datsuns), of which some parts are compatible with the British SU's. I'd like to get a pair of velocity stacks/air horns for them, but I don't know if the inlet diameter matches up. The Hitachi SU's inlet diameter measures 35.8 mm....not to be confused with the butterfly or throat diameter. Can anyone tell me the INLET diameter of the British HS4 SU? This would also correspond to the velocity stack final diameter. -Thanks