RE: Quique's 72" Yak 54
I now have both of them. They are built differently. Both are very well built ARFS. Quique's Yak is less scale. They say it is semi-scale while the Extreme flights Yak is much more scale. I am now finishing up the Extreme flight Yak and should test fly it in a week or so. I will start building the other Yak after the Extreme one.
IMHO, I would not put a gas engine on either of the planes. They both would be too heavy and you would probably lose all the good flying characteristics of the airplanes. Neither are built to take a gas engine.
I am running a YS 1.10 in the EF Yak and I am still up in the air on the other Yak. I have a YS 140L and a OS 160. Quique flys his with a YS 140 sport. In the instruction manual he says a OS 160 is also a very good choice for the plane.