Also how far past the MAF does the inlet pipe have to remain at 3". For example the turbo inlet for my 18G is 60mm. The MAF is 3" or 76mm. If the inlet shrinks down too quickly, does this have an impact on airflow?
 
I have mine tuned by JBS with a S3 3" MAF, Im at around 450hp.
I did have a 4" MAF housing for a VR6 but was told it was too big..
 
Also how far past the MAF does the inlet pipe have to remain at 3". For example the turbo inlet for my 18G is 60mm. The MAF is 3" or 76mm. If the inlet shrinks down too quickly, does this have an impact on airflow?

i think the reducer on turbo intake itself is what I would do so 3" as far as you can to turbo intake.