The four stroke did help out getting the correct CG but any good two stroke .60 will fly the plane. I remember that I had just bought that engine at a club auction for $100.00. I knew the owner and the history of the engine.
What four stroke to buy will open a can of worms. I think Magnum and ASP are total crap but others will swear by them. I also think OS has priced themselves out of the market. Today I pretty much use nothing but YS and OS four strokes and the smallest I have is the .91. I really like the quality of YS and OS with Saito coming in a far third place.
With this being said I would no longer bother buying a new glow engine. We have too many good little gas engines on the market today. IF, a Capital IF, I was going to go with a glow engine in my Decathlon today I would just buy a new SK .91 two stroke from Kangke. Other then one, I have had good luck with the SK engines. They break in a bit different then other brands and there instructions that come with the engine were written for another engine a long time ago and are not correct!! They are still a very good choice and only $100.00 for a .91 with a muffler.
If I couldn't afford or didn't want to spend the money on an OS four stroke then I would just buy the SK, low RPM and high torque engine.
YS is a great engine but not an engine I would tell everyone to go out and buy. I think they are idiot proof but I have been proven wrong!!