Are severe duty kevlar belts available for this clutch?
what about adjustable clutch weights?

obviously you are getting the belt too hot and are on the right track in trying different springs and weights to get it tuned.

on my turbo RZR I tried a stock belt and it blew in less than 100 miles. EPI severe duty belts were lasting about 600 miles. The belt on the Redline is a lot bigger than the RZR belt...