Len,
you need to talk to Branden Wheaton.. He is the only one I know of that Reverse Enginered a Mount and converted his N5 to an E5. It was Pretty impressive. In regards to the Question, off the top of my head the first thing that comes to my mind is Frame Width. Next would be Motor Placement. Get with Branden and I'm sure he can at least answer a few questions and possibly Stear you in the right Direction. Good Luck and Keep us Posted.
Kevin