Unless you have a few other mods, as well as a good running motor (not needing any standard maintenance) I'd suggest no more than a 3.5.
The mods you will need at the very least for that:
Cold air or Fenderwell intake
High Flow catalytic convertor
colder spark plugs (autolite 104'* area good one and gap them around .054"-.057")
Also, a scan is always a wise choice. It may tell you whether or not your car needs ported exhaust manifolds or something else.
And one thing for sure, ESPECIALLY when changing from a stock pulley -ABSOLUTELY NOTHING SHORT OF PREMIUM UNLEADED FUEL -no regular or mid-grade or you'll more than likely melt a piston.