For what its worth...I am just finishing my UltraStick with a K&B 61 and it looks like it will balance without adding any weight to the tail. The K&B is very light and I used a Dave Brown glass filled 40 size engine mount that fit the K&B perfectly. I also used a custom and very light muffler from Bisson.
http://bissonmufflers.com
I'll put some pics up tommorrow if you like.