Here's the problem with "non slip" pulleys. They work well and do what they were intended to do.....but only to a point. If your belt is just on the edge of slipping with a standard pulley, the non slip will help....but if its slipping badly with your current pulley diameter, its still likely to slip with the "non slip" style pulley. There problem there is, the non slip pulleys tend to act like meat grinders when they do slip and will make short work of your accessory belt in a hurry. In your case, that's a bad thing, because you're running a single belt system. I would seriously consider just bumping up the blower pulley diameter for now to reduce the slippage....and if you don't think it's spinning fast enough, save your pennies for an overdrive crank pulley. Innovators West, or ASP may make something to fit your needs. The problem with this, is that you may run interference with your water pump pulley. I believe the Cobra water pump pulley may be a smaller diamter, which will give you a little more room to grow on a crank pulley....or you could forgo a water pump pulley altogether and run an electric water pump. Anyway you slice it though, it's going to cost you money.
I personally think a major reason an M90 kit for the 5.0L OHV engine didn't take off wasn't so much performance limitations, but packaging. It's just so much work trying to get than little sucker to spin the way you want it to. An MPx case and inlet when spun hard enough will easily keep up with any of the horsepower capabilities of the twin screw offerings for this engine......but spinning them as fast as they need to be spun can't be done without an independent pulley system.
My only other suggestion to help control belt slip would be to convert your entire set up to an 8-rib pulley design, from the current 6-rib. This will add some traction to the pulley as well as open you up to some of the pulley offerings the Supercoupe guys have. If your blower set up was independent, you could even consider a cogged pulley system....but they've got to be darn near perfect alignment was and completely flex free to work on the street.
