Yeah an 84" brush cutter would likely be too much for that tractor in the thickest of material. While not exactly apples to apples, I have a 72" brush cutter on my rebuilt farmall super m, which is rated at ~50hp at the pto. I can stall the tractor out when brush cutting ridiculously thick scrub brush. I have my rear wheels set in about as far as I can and is still wider than the mower by a few inches so I have to overlap on ones side when making multiple passes if I am worried about it. Usually dont because its usually just used for clearing back deer trails or shooting lanes. Again it isn't an apples to apples comparison to your much more modern diesel kubota, but it's the only reference I have...