RE: 69" QQ Yak-54
A 180 would be overkill. Guys will start putting heavy motors in the plane, then complain that it doesn't fly well because they have over loaded it just like has happened with so many other planes. If you stick with the recommended engines you will be treated with a light, properly loaded wonderful flying plane as it was designed to be. The Saito 125, O.S. 120 and YS 1.10 should all be perfect matches for this plane, I see people ruin the good flying characteristics of planes by doing this and it's upsetting considering the time that has been spent with the designing of these planes. Watch the video of Reza flying the plane, that motor is new and still breaking in and has what I would consider more than enough power.
Lee