It'll fly fine with an 80, but it won't want to land. I had a 4-stroker .91 in my 60, and I could never get the throttle down enough, to get it to stop sailing.

Trainers have a large wing area, and dehidral, which means it'll glide for a long time. When you put a larger engine on it, than it's called for, you have to increase the recommended propeller, which leads to more thrust. In short - if you are going to go large with engine, get a prop with less bite. 12x4 or something.