I seen the pics on E2S, and I'll tell you right now that building mounts off the factory mounts won't work...
I tried that twice before I gave up, and just welded my own mounts in the frame. Also if you don't use the rear mount off the swingarm, the head won't clear the factory fuel tank. (Which means modifying the swinger)
You'll also have clearance issues with your head pipe. Which can make mounting the expansion chamber a real bitch...
I can also tell you that a 465/490 pipe off a bike will "not" fit the warrior frame without serious modification.. The TRX250r pipes are a great fit, and the expansion chamber designs are really close to the same.
Just my $.02, but I have been there before. It took me a long time to get that damn 490 in my quad! lol