Step 8 - Pipe
Of all the steps, this one is the most difficult or simple. It's simple if you can purchase a Service Honda (no longer being made, but available on eBay), DynoPort, or any other pipe made for conversions. They are bit more expensive, but may be a break even when you consider the price of buying multiple pipes to craft together, welding time, frustration, years off your life, etc. If for some reason we are in an apocalyptic future where these pipes are no longer available, then your only option is combining a KX 500 pipe with a CR 500 pipe. This sounds simple, but be aware that the CR pipe hugs very tightly to the KX engine and will need lots of hammer adjustments to make it fit. Be prepared to do mean things to your pipe. Your main area of interference is the coolant transfer from the water pump to the cylinder head. You will need to dent the pipe pretty heavily in this area. I have seen people use a trick Service Honda employed where they flip the fitting and use a special hose to come in from the top. You will need to do search of the site to find this trick.
When you get your pipe finished, do yourself a favor and spend some time on the mounting bracket. It will need to be beefy to handle all the vibration. While you have the motor apart or the electronics safely out of the motor, you have the opportunity to weld on some beef to the mount. It doesn't need to support a tank's weight, but it does need to be beefier than the 250 mount. You don't want your pipe coming off. I used some 3/16" plate and a solid rod that I threaded to accept the 03 250 half rubber mount. So far my pipe is still on.
My pipe was a KX 500 inlet, and parts from a trashed CR pipe and a good CR pipe. I used the trashed CR pipe to add material to push the pipe out near the interference areas (ignition cover, transfer pipe). I added about 1 1/2" in the front bottom, and a 1 1/2" to 1/2" wedge in the front right above the engine exhaust port (the thickest part faced mostly forward). The wedge turned the pipe out a little bit as it came around, giving me a little more space in the transfer pipe area. Even with all that I still had to dent my pipe. This is a trial and error part, and will require some decent fabrication skills. Did I mention that people make pipes for this conversion?