Maybe I'm missing something -- but I'd go 'smaller' -- 72". Just work on one-half at a time. I would think about cranking one of the arms out to set the blade at an angle to get the crown that you want. Make two passes -- 1 in each direction. You mention that this is an established drive. I did a lot work on our church driveway this summer -- with the knives set way down. It brought up the ground-in stones -- people stopping in thought that we'd already had a load of new rock delivered -- but we hadn't. The knives bring up the rock (takes several passes).