Rebuild it first. I added a pipe and reeds after 700 miles and really didn't notice it. Added the head to complete Stage III over the summer and had multiple issues. Pulled motor apart to find piston and ring damage right where the intake charge comes in. I believe, and I may be wrong, but I believe I did the mods after the damage was there and that is why I didn't see any increase in power. Put sled back to stock after rebuild since I am going to get a 13 anyways. No use selling it with the kit. Sled runs great now.
After you rebuild, turn up the pump about 3 turns, and run oil in your tank. You should have no problems...if you already run extra oil, have at it and enjoy the power.
I rode a Stage III kit last weekend and it was noticably different than stock, which it wasn't on my sled.
SLP makes good stuff.