I have that same pulley/belt combo on my 90 SC. You will need a larger idler tensioner pulley on the tensioner for the SC belt or you will very likely get some slipping. Mine didn't slip for about three months but then would start slipping at high rpms.
I have the following mods on the 90. Supercoupeperformance CAI, 73mm MAF, Racer Walsh Pulley (10%+), no resonator (Custom Y-Pipe out of stainless steel) and two Magnaflow SS mufflers.
I get a solid 15 lbs of boost at 5,000 rpms. The pulley/belt combo from Racer Walsh works very well. You will feel a seat of the pants improvement. Don't run this pulley with the stock exhaust or you are asking for HG trouble. I put the pulley on and immediately drove to the exhaust shop for the Y-pipe and mufflers to be installed.
Bob
