I have a Townie as well, and I must say it is a very comfy ride. I have thought about installing a 2 stroke in it, but have decided to go anther route. I will be picking up a GEBE. Having a 4 stroke and not having to put up with the chain tensioner sounds like heaven! LOL
I look forward to seeing your build. Here is a pic of my bike. I have yet to order the GEBE kit, but I will have it soon.