Laker, I have seen people do well before with the boxer. I'm sure you will like it. As for props, I have never had the ys 61, but I have had a k&b 61 twister and I used a 13x8. You best bet is to go into the engine manufacture forums and go to the ys forum and ask Dave Shadel. He'll answer you pretty quick. I have seen the extra do ok in sportsman class also. I flew an ultimate bipe once in sportsman.

Woops, I hear good things about the os160. I have the os140rx in a 140 sized Zen 1st edition. I love how easy it is to run it. Way less tempermental than my ys 140's. I don't know if you know this but here ( http://www.gatorrc.com )you can get plans for 26 dollars to the gator typhoon 2000. It's a design that did well about 6 years ago. There are still people flying them, and I feel that they fly and present pretty well. Maybe it would give you something to base your plane off of. I know it did for me.

Krishlan