Inlet/outlet diameter on standard bov

[neil_jdmr]

changing my bov and already have a hks ssq which iam gonna adapt to fit
but as above, as the inlet on the hks looks bigger and gonna have to reduce it and block off the side going to the airfilter.
 
 
Inlet size required Please
 
Have tried searching but came up with nothing although it was a bit of a half arsed search as Im at work and will get my collers felt.
 
Thanks