Never built one myself but the ones I've seen were either Cox TD or Norvel powered. I'd go with the Big Mig. Don't worry about the prop/cowl issue...it's not a problem. The extra weight of the .10 would make it nose heavy and your wingloading would go up as well. Definitely uncool.
ps: Having said that, 14 other guys'll prob'ly come on and say the OS.10 is a perfect engine for it!
