How about an update on your Sportster 120? I'm putting one together now and plan to use an OS 120 Surpass. What did you come up with for final weight? The more I read the instruction manual and addendums, the more I noticed the concern for a solid tail attachment and tight control surface setup. I'm trying to make flutter less an issue by putting counter weights on the elevators and rudder. It doesn't completely balance the surface but I believe that what I did will help.