2005 GP GT Top Swap (L26)

ZZP SSIC (1in core)
Intense S2X Cam
SSAC Headers no cat
60# injectors

other supporting mods.

I wanted to do a drop from a 3.5 to a 3.3 pulley but have been told by a few people that I will be safe on a 3.1


What size pulley should I get for the 3.3 and should I go to a 3.1? What size belt would I need for that? Keep in mind I have the 1in SSIC

help me maths.