Look at your Kubota Operators Manual. There will be a page where Kubota recommends the max size for major implements.
Like most manufacturers the recommended max is pretty conservative. Liability and all that crap.....
Mine says for flail mowers - 120" wide (max) and 1780 pounds (max).
That would allow me to operate a flail mower larger than my wildest dreams.
Also - a whole lot larger than my pocket book.