Well after speaking to quite a few people who own the Katana 50 I decided to go with a large 2 stroke, I have a basically brand new OS 91fx, or a very lightly used Evolution 91nx that I did a complete tear down and clean, both motors weigh about 24 ounces with muffler.
when I do finally build the Katana I will be looking for any flaws or weaknesses in the airframe to make sure it holds up, the OS 91 is a super smooth running motor so I'm not to worried about vibration.