The YS 91 and Saito 100 will fit quite nicely; got one of each at my club. Both engines are perfectly matched to this model. I have a YS 91 that wil go into mine.

The YS 91 with an APC 16x4W has lots more vertical capability than the Saito with a 15x8. The guy with the Saito is going to try some different props. We've tried a few on the YS, and the 16x4W seems ideal.

Dunno about a YS 120.

Steve