In the above pic, post 2, you can see how much wider the maxx arms are compared to the Slash bulkhead. When it comes time for final assembly they will have to be dremeled down for the pins and brace to work right.
The final width from Wheel hex to wheel hex is 14.5 inches. About 4 inches wider then a stock Slash. Here it is next to my E-revo

While it looks much wider, when everything is in the proper place, they are almost the same width. The wheelbase is unchanged.