I have the river raider expedition one on mine. Slightly modified though, I had a custom intake made for my LS 6.0 that keeps the snorkel functional.
When I first bought it I had the stock 4.0 and used their mushroom style cap. It's basically the same as some of the cowl intakes users have out together themselves. Just the execution is slightly cleaner.
I later added a Ripp Supercharger and bought their snorkel adapter kit. The kit basically consisted of a k&n filter with a threaded stud on top and a lampshade style cover.
Since sold the Ripp for an LS but kept the snorkel.
During the tuning phase the tuner used both the snorkel and just attaching the filter to the intake tube. No noticeable affect or loss in power until you got into upper 5000+ rpms. Did note lower IAT's with the snorkel.