2.5" is the right size, or the stock 92/93 pulley (2.55, essentially the same).
You'll wish you did an intake or at least vent your airbox and drop in a performance filter. I also strongly suggest a 180° thermostat at the LEAST.
You'll have snappier throttle response and higher boost, but won't benefit completely until that intake is fully upgraded with a pipe and cone.
Buy the stock length gatorback belt, oversized tensioner pulley, and consider changing your coupler at the same time as a preventive measure.