Hey Dan, you should be able to use an existing harness and just use the connections you need. This will save you a lot of money as those "done" harnesses go for around $900. This guy over on cuda-chllenger modified the original harness, plus doing a number of "home brew" stuff like you are planning. Here is the thread....
http://www.cuda-challenger.com/cc/index.php?topic=89416.0I PMd him to see if he finished his spread sheet on how he did everything but haven't heard back yet. Another member his trying to get me his CAD drawing for the 518 trans cross member that he had fabbed up.
I can forward you the info once I receive it. Also, once you have the mounts down pat, would you be interested in making a second pair in which I could purchase off of you, or work out some kind of deal for a pair?
Thanks