I have a B2620 and a 4ft Walco brush hog, the tractor is a little bigger than yours but I'm not sure that you can get a brush hog smaller than 4ft. My tractor seems to handle the Walco quite easily.
You'll be just fine, alot of impliement companies are seeing the need for toys right sized to match the sub compact tractor market. So there's a whole line of attatchments build just for the needs of sub compacts.
Bush Hog has a series of rotary cutters called the Squealer Series and I believe it is the SQ142 that will work on the BX1860, it has 10 HP minimum power requirement and is 42" wide.