Do us a favor and put your model, trim, and year in your sig so we can tell what you have. If you have a series 1 engine ill defer to those guys to guide you. If you have a series II you will want to start with a 3.5 or 3.4 inch pulley. You may also want to invest in a scanner of some sort so you can tell if you start to get knock (which you will most certainly have with a smaller pulley). Also if you step down a pulley size, I highly recommend a 180 T-stat, 1 range colder plugs, and a CAI or FWI (not just a cone filter setup)
Edit, just re-read your 94 SSEi, so your series 1. 2.8 I think is the size? Bill?