You can adjust the lever so that it won't lock in reverse and Gravely made a modification to later 7.6 tractors that does the same thing. "Hilly" isn't a problem for a Gravely, but "rocky" means you should be using a sickle bar or flail mower instead of the bushhog.
My problem was I needed the leverage of the bars to maneuver it while walking backward (the topography demanded I go in forward, move it around a bit, and back it out), and it was very difficult to hold partial reverse (I assume I was slipping the cone clutch ) with my right hand while also trying to lever the bars. I had lots of more open area where this wasn't a problem, but here in CT you can't go 3 inches in natural soil anywhere without a flat, big, sharp tip of a rock pointing out of the ground to trip you. I was always stumbling backing up, afraid I was going to trip and that thing would chop my legs off.
But I loved it! Had the dual-wheels that were great for floating in the marshy areas in the spring to knock down the brush before waiting for August for it to dry out. I am just really impressed with the level of home-grown USA engineering that went into it and allowed it's design to remain un-changed for decades. May own one again some day, have fun with yours!