I use the 3-point to tow trailers on a regular basis, both with the M6060 and MX6000. I use the KingKutter receiver shown below and run a chain from near the top pin to a shackle on the draw bar to prevent the 3-point from lifting up more than I want.
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Perfect solution. Anything to keep that hitch point below the rear axle so it doesn't take the weight off the rear tires. Loading the trailer toward the front is a good idea, too. It's gunna take a woppin' big trailer and load to push a 6060 or 6000 around, but still a perfect solution.
I like your KK hitch. The one I had wasn't QH compatible, so I had to make a few mods to it. Sure is nice to not have to pull the QH to move the trailers. I need to get a clevis for my draw-bar and copy your technique now that I've modded the 3P hitch. I don't need the trailer ball in the drawbar anymore now, especially if I do the same as your photo.
Still, the tires do grip better in the forward direction (pulling) than they do in reverse [by design, of course], which can still lead to a break-away and jackknife on a particularly steep slope. They are not designed for sideways traction at all. I've had 'nekked' tractors slide sideways in the right soil conditions (wet clay) for no apparent reason other than a tiny bit of slope to one side. A trailer will QUICKLY aggravate that going down hill. But that could happen just as easily with the trailer connected to the drawbar, and has little to do with the COG. It has more to do with traction. The trick is to make sure to keep the tractor in front of the trailer, and the tongue below the rear axle. That may mean going a bit faster than you wanted to, so it's best to start off down a steep slope REALLY slow to begin with. It's a tractor, not a race car.
I pulled hundreds of trailer loads of green firewood in a trailer behind a Cub Farmall which while empty probably weighed twice what the Cub Farmall WITH wheel weights did. The trailer had a steel frame made with 3-inch angle and 3" well casing for a tongue, 1/4 inch thick stainless steel sides and bottom, and had pretty good size truck springs under it. That thing was STOOPID heavy. My step-dad built it while working at Brookley AFB in the early 60's, and his worst omission was a tongue jack. The tongue weight on it was almost more than I could lift to hitch, (and probably couldn't now) so that was actually a good thing. I got into some spooky situations with it on more occasions than I care to remember. That thing was HUGE, and what I learned to reverse trailers with. I was never overly concerned if it pushed the back of the Cub to the right a little, but if the back end went left, the pucker factor went up. A Cub will flip to the left in a blink with the offset engine. And there weren't no roll bar nor seatbelt. Just the 'jump' training, which probably saved my life on more than one occasion, too.
We had a rig to connect the top link on the 8N down to the 3-point draw bar to keep the link arms down, and I usually used the 8N if my step-dad cut firewood up on the hill. But that rig was a PITA to put on the 8N, so if I didn't have time to plan for the hauling (told where the wood was when I got off the school bus), I would put the trailer behind our old '46 Willys' MJ-6A and keep it in low range 4x4 with the switch turned off for engine braking. If the RPM got too high, I'd just find a pine tree and stop it, because that old Jeep NEVER had any brakes on it. Wide open in 3rd gear high range was only about 28 mph anyway, so it was geared lower in low range than the tractors were. I could walk faster than it would move in 1st gear low range at redline RPM. Mud ate the brakes up too fast, and we never drove it on the highway, so we never bothered to replace them. He wasn't impressed with me when I exploded the 3rd muffler when I turned the switch back on at the bottom of the hill. Somebody probably played with the throttle a little on the way down the hill and got some unspent fuel into the exhaust, which promptly ignited when the first cylinder fired an exhaust stroke into the manifold. Sounded like a bomb going off. Don't know how that coulda happened. He quit letting me use the Jeep. No sense of humor, I tell ya.