A Saito 1.20 would be way too much power, also you will get more vibration from a larger single.
A .91 4 stroke or .75 2 strokewould be more suited to this plane. Mine has a Saito 1.00 and I rarely go above 1/2 throttle. Also, with a larger engine, there is the potential to fly too fast and induce flutter in the rudder resulting in a forced reunion with the earth.