It's always easier to have the engine or motor on any build, not a real must have but if you haven't built before it is best. Last four stroke I used on one was the Saito 100. Unlimeted vertical is really streatching it a lot. With the YS 1.10 that is a true statement. I have also used the Magnum .921 and the OS .91. Last one I built was a full wing total stock build other then the angle stock behind the fire wall and reinforced LG block as Seamus mentioned. In two stroke the OS .75 is a great choice but any .60 is fine in that plane.
I use the plane to teach building with so I have used a bunch of different engines over the years. Ed Moorman did a kit bash on one to make it look like a warbird, one of the cooler builds I have ever seen.