Revo with centerdiff unloading

All this talk about center diffs has got me interested in getting one of the "Cowboy" ones as shown in the ebay link and here. Cowboy said he has no interest in making any more, but did say he has no problems with other making them and even offered to provide drawings. Has anyone taken him up on the offer? What is the one Griffen is doing? I'd like to have a real center diff in my Revo