I was wondering what size would work for my tractor.I have a couple 1/2 mile long roads to tend to and I think this would be much better suited to do the job than a box blade.
As far as size, it really depends on how much material you end up moving.
My tractor is 60HP, and weighs double what your Kubota does.
In this pic, I was moving so much material, I had to use 4WD,,,
it was the first attachment I have ever used that made the 'ole IH "snort"!!
The LP is 7 feet wide.
It is new, and I need to adjust the blade height, that will happen in a couple months.
Right now, I simply adjust the 3PT hitch to keep the left side up an inch.
If you look at the left runner, you can see it is not leaving a track.
The right side leaves a track an inch deep.
So, I guess, if 6 feet is as wide as your tractor, I would recommend 6 feet.
You definitely want one at least as wide as the tractor.
BUT, expect a 7 foot one to be able to stop your tractor.