I run a 6" Pro-Comp lift on my 2K SD and there was no need , in my case for a spacer. The kit consisted of front and rear 4" springs, a front leveling kit and rear +1" block. The leveling kit gives an additional 2.5" of lift. I did however have to lengthen the track bar about 7/8 of an inch to let the front end travel correctly. If you lack the tools or ability to make your track bar longer then an adjustable one can be purchased from Skyjacker Suspension. I would have went that route but they are VERY overpriced !
I also had to put rear air bags on as the Pro-Comp springs work good offroad but killed the hauling/towing capabilities
Good luck, Jeff