I modified mine. Took some time but it works. I used all exsiting parts and put all three wheels on the inside. Only had to buy some washers for the outside. I like the idea of having three wheels instead of two. Just make sure u measure twice before u cut your stock shaft.
I bought mine from Mountain Magic.
I modded my last stock rear axle, and I found it was easier and less time consuming to just buy one.
Just remember that 3 wheels are better than 2, especially when one fails 20 miles back from nowhere.
I have found no advantage other than bling with inboard wheels.