The website is www.spadtothebone.com. I think it's under the plans section, but you may have to hunt for it cause they recently changed the site around. I measured the inside of the front portion of the muffler and it's 7/8" in diameter. I found some 3/4" outside diameter aluminum tube, but the walls of it are kind of thick. Will this matter? Will it be too heavy? Should I use 3/4" outside diameter tubing for the 7/8" inside diameter of the muffler?