So I finally bit the bullet and went for the Clayton modification on my 2006 Honda VTX1300C. In this posting, I outline how I did it, with pictures, and "before" and "after" videos. To be honest, it's not as loud as I'd like, but the sound is much deeper and I like that a lot. My biggest problem was a drill with too little power. The 1/2" drill bit did not want to turn through the metal plates. So what I've ended up with are 7 3/8" holes in the outer plates, with the bottom (or 6 o'clock position) being 1/2" going through both outer and inner plates. Please wear safety glasses whenever you are drilling. Also, it'll help to put down a drop cloth, or a large piece of cardboard to help catch the metal shavings. They may be small, but they can still hurt.
Also, please keep in mind, I am NOT a mechanic of any sorts. So please understand you are completing this modification at your own risk. I did this only because I can't afford a new 3rd-party exhaust system right now. This will certainly keep my happy until such time as I can afford a Vance and Hines or similar system.
Before:
After:
Here's how I did it:
Here's how the exhaust looks without any modification:
Step 1: Place painter's tape around the outside and inside of the chrome, to protect against dings from the drill. Then make as many markings with a Sharpie marker as you want. In this case, I chose 7 holes, at positions 2, 3, 4, 6, 8, 9, and 10 (as in a clock face).
Step 2: Drill 1/8" pilot holes in each desired location, as previously marked with a Sharpie marker.
Step 3: Start increasing the size of your holes in any manner you choose. My drill isn't very powerful, so it helped for me to use increasing bit sizes until I reached my target size, which in this case was either 3/8" or 1/2". There are varying opinions on "going deep". There are two plates to drill through: the outer and the inner. I only drilled "deep" (meaning through both outer and inner plates) in the 6 o'clock position. You can do whatever you like, and I may, in the future, decide to drill through the inner plates in more locations to increase my volume and the depth of the sound.
Last step: Finish drilling your desired size holes, and then repeat the entire process for your other exhaust pipe. Remove the painter's tape and vacuum up all the metal shavings. Fire up your baby and ride!