BobS, with the measurments given by O.S. a 90 4-Stroke is almost an inch outside the cowl (inverted). I can make a 90 2-stroke, Supertiger, fit inside the cowl. I have a 70 O.S. 4-stroke, and it won't fit inside the cowl. I'm sure a 60 would fly the plane nice, I would just like to have the sound of the 4-stroke. I hope to make it up to Oshkosh someday.