GM doesn't sell couplers. And a smaller pulley would help you but only if you've done a good intake and the 180° themostat already at the least. Exhaust is preferred as well.
For a lightly modded car, I suggest a 2.3" pulley for a 92/93, and you MUST use the oversized idler pulley to get sufficient beltwrap and prevent slip. 2.5" or the stock 92/93 pulley would be for the 94/95 performance. Oversized tensioner is suggested for the 94/95.
You need to order your coupler from ZZPerformance, and the oversized idler as well. You can get the oil from the dealer. You only need one bottle for an M62, but you may need slightly more and should have some on hand. You also need:
1 little tube of red 'gasket maker' from the dealer to re-seal the nosedrive
1 Supercharger outlet gasket (dealer or Fel-Pro)
2 Yellow coolant bypass o-rings that go between the SC and LIM
You also SHOULD get a TB gasket so you can remove it and clean it at this convenient time. Fuel injector O-rings would be good now too, since you have to pull them anyway.
On a Series 1, you'll need to pull the ENTIRE SC off the car. Series 2 doesn't need to. So pull your SC cover, fuel rail, double-nut and remove the stud from the SC nosedrive that goes through the alt bracket (after removing the alt), then remove the throttle bracket, and remove the SC and TB as one unit. Seperate them after removal from the car.
For a newbie, this should be a 6 hour job at the most. We have alot more info for you as you get ready to do it. Including the following links (this is for an M90, but with the instructions above for the Series 1, this will get you the rest of the way) Torque specs are in Techinfo, Specifications.
My first coupler 3 years ago (M62):
New coupler and idler from ZZP:
Pics of the oversized idler comparison. Oversized installed, stocker held in front for reference: