Crankset chainline: 45mm http://bike.shimano.com.sg/publish/c...3.-type-..html

As far as the ENO's ability to take up chain slack, I kinda doubt it could accommodate a 2-tooth difference in cog size. I have an ENO on my mtb and from memory it doesn't seem like it has sufficient range of motion for that kind of change in gearing. Although I have never tried that and I could be wrong...

However, wanting to flip your wheel plus have a dingle cog sounds like you want a lot of gearing options. Fixed gear doesn't seem to be the best choice here.