He is talking about the FMF Gnarly desert pipe.
Here is the link to the RB site:
http://www.rb-designs.com/
Under carb mods and head mods you will find the KDX.
I think he explains what the mods will do on his site.
I don't know about gearing, I haven't done any yet.
I have a 2005 KDX 220
here is a list of mods/upgrades I have done.
-FMF desert pipe
-FMF Q silencer
-Boysen Rad valve
-Wiseco piston
I just removed the airbox lid snorkel, but I here that its better to remove the entire lid.
I also have a E-Line carbon pipe guard on it's way.
I find that these changes really improve the power overall.
I don't notice any loss on the bottom end. As long as the pilot circuit is set right it works great.
I don't really do much riding above the mid rpm range but on any straight trail it goes quick!