My engine just arrived. Its actually a Mark 61 that I got off Ebay for about 100 bucks new. I kind of wish I had picked up two for that price. This is a beautiful piece of machinery to behold - makes my 61FX look like a high school shop project. The box says made by Moki in Hungary and the seller verified for me that it is basically the EXACT same motor. My first test will be with an O.S. 61 muffler and then a with tuned mousse can and then a pipe. I think I'm going to prop it and set the pipe for torque so I can see if it comes anywhere near some of the other LS pattern engines like the YS or O.S. RF. I know a cheap punched out 90 like the ST will out pull it but the intent here is to abide by displacement constraints where applicable in the sport. Any one have suggestions on break-in for this engine? Its got a ringed piston but with a brass chromed liner (also, vague instructions). It doesn't have a pinch at the top - so I'm guessing the typical ringed break in will work?