Cessna, An inverted four stroke is a non-issue. (two strokes are a horse of a different color). My personal experience is that a 72 is slightly smoother than an 82. Prop clearance might be an issue. It has been a while since I've had one of the Agwagons in my hands but I do not believe a 72 would be too big physically. Maybe one of the new 62's would fit your purpose.
Fred