Siclebar is the best choice. I have a little self-propelled Troy. Ever see the big tractors with the siclebar booms offset to the side of the 3ph grooming alongside the highways? The bar is easily tilted to be parallel to & above the slope. When you get to an obstacle, just lift the boom, pass, lower again. That'd be my 1st choice.
Something that might work (but wouldn't be my choice) is a flail mower offset partially to the side. They are, however, heavy, expensive, off-balanced, and complicated. The little ones for a BX are about the max. weight a BX can take and do not extend very far to the offset side. I only mention this because some highway maintenance crews do use them. Still, it's probably the worst thing you could choose.
I have a rough cutter to cut several acres of tall weeds. Since I only have a small amount of banks to trim, I back the BX up perpendicular to the very edge of the streambed and allow the cutter to hang suspended in the air over the stream. I then gently lower the cutter to the appropriate depth, raise it, reposition, repeat. I do this from each side of the stream. It's slow, but with only a little to trim, it works. Mine is 42" wide, same as the BX. A 22 horse BX MIGHT actually be able power a 60" rough cutter. That'd give a 9" overhang on each side of the tractor running parallel to the stream. For some people with a small stream, it could be a choice. You obviously need a lot more than that.
