I just acquired an OS .61 SF that has little or no run time. I am trying to decide the proper method for run in. I am not sure whether it has a ringed piston or is ABC. When I look in the exhaust port, I can see a line about 1/8" down from the top of the piston. I can't determine if that's a Dykes ring or just an oil groove associated with an ABC piston assembly. Also I have a later E-4020 long expansion style muffler that I was thinking of using in place of the short muffler that came with the engine. I'm wondering if this might be a good choice as I know the engine was designed with a tuned pipe set-up in mind for F3 pattern. My use will be for sport flying and I plan to prop it to run in the mid 11,000 rpm range. Can one of you old school gurus help me out with the correct combo/tune. I'm guessing 12-7 or 12-8 prop running on 15% nitro-18% oil with 2-3% Castor would be about right?