No Problem; I run a 72" with my 970. Might be some differences in tiller makes, but they don't draw all that much HP. I normally run in 3rd low for 1st pass, and 1st medium for the second, which scoots right along. Think about it; I used to use a 24" walk-behind rototiller with a 5 hp Briggs that moved along pretty good. Three of these would be 72" and 15 HP.
Also depends how deep you want to go.