I am about to order a shoestring and have been researching this site for info. Also trying to decide on engine/muffler. I plan on flying scale- like aerobatics, and laps around 100 mph. Want to use a 2-stroke with a Pitts style muffler.Slimline and Bisson both make mufflers which fit up to the OSFX .61 and .91. I think the .61 may not be enough. The .91 is actually a tad lighter, but i keep hearing about problems that some are having with the .91 leaning out either due to lack of backpressure from the muffler, or O-ring leakage at the carb. I am also considering the Tower .75 ABC which might be the perfect size for this plane, and am told that either the Slimline or Bisson large chamber for the OSFX.91will fit up to the center mounting holes with a little filing but the exhaust port and muffler opening are not the same dimensions,and don't know it it's worth worrying about. Still researching. There are a number of shoestring threads on this site that you might want to check out. Go to search on the ARF page and type in GP Shoestring. And yes, the main gear should be canted foreward.