I bought some Gen 1 Viper caliper years ago with intentions of using the Dr. Diff kit. I ended up putting the car back together with the FMJ 10.95" discs I had just to speed up getting the car back on the road. Now that the car is back together and has about 1500 miles of getting new build bugs worked out, it's time to start upgrading things. I decided against using the Dr. Diff kit and make my own. My first course of action was to measure the arc on the caliper to determine the maximum diameter rotor that could fit in the caliper. I wasn't able to get an exact measurement since the top of the caliper is open, but I got it close enough. By the magic of geomtery, I determined a rotor diamter of 13.25-13.5 would work. After way too much time researching rotor diamters on rock auto, I decided to start with a 13.25" modern mustang rotor as a test piece. Before I could test the rotor, I bought some 10.95" rotors and had a friend turn them down into hubs. I picked these up from rock auto for $25/ea. My calculations to determine the maximum rotor diamter appear to be close. all of this looks great, until I figure out my wheel won't fit. The spokes hit the caliper... bummer. At this point I went back to searching for another rotor with a higher offset between the brake surface and the wheel mounting surface. During a convestation with another member on here, he recommneded I look at the 2010 Challenger RT rotor. This rotor. The offset on the challenger rotor was about .25" greater than the mustang rotor, and the diamter was slightly larger at 13.6" It looked like it would work, so I moved forward with designing a bracket. Since the car already had the FMJ spindle, I figured it would be easiest to design a bracket using those spindles instead of a drum spindle. After some measuring and cutting 3 different samples, I arrived at this: It's a very simple design and would require about 1/4-3/8" worth of spacers between the bracket and the caliper. It was hard to determine exactly how much since the wood crushes when tightening. The wheel fit too, but would likely require a 3mm spacer for some piece of mind. And why not compare the difference.. I had a buddy convert my hand drawings into CAD and I sent the file to sendcutsend.com. I was amazed at their customer service. If you need anything laser cut and don't want to deal with the minimum quantities many local companies have, I suggest this company. They were great! Test fitting everything with the new brackets: Turns out a 3/8" spacer would be perfect. At this point, having a wheel spacer was really buggin me. For some reason, I decided to look at the rear rotor on a 2010 Challenger SRT. It has a really high offset, almost 1/2 more than the RT front rotor. This was good. The diamter did get slightly bigger again, up to 13.7". I figured I'd give it a try, so I picked up a rear SRT rotor locally even though I was apprehensive about the diameter exceeding what I thought would be the maximum for this caliper.