Tim, if you remove the starter oil will leak out of the gearbox, plus the casting is larger on the starter side with an idler gear in the housing, so it does interfere with a prerotator.
I did the same thing. I contacted one of the larger Rotax suppliers tech guys to see if they woule take a trade on my E-box. My E-box was new/ "0" time, even though it was several years old, no power had ever been applied to it. I traded even up for a new C-Box. I also had several replies on Barnstormers.com when I posted it there. If you make some one a good deal on a swap for an electric strart they will take it.