Your ditch sounds like it could be done with your blade just fine as long as there aren't any larger roots or stumps/rocks etc. in it. I normally drag the ditch with the boxblade tilted as far as I can until I get a good box full, stop and drop it, get it out with the loader, get back in the ditch and continue on. When you get down to the final grading you'll be able to drag a long way before having to use the loader to remove the pile. Your tires will help pack the very bottom of the ditch as you go too, then you can seed or rock your ditch as necessary for your situation. The max. tilt on most boxblades will give you a nice, gradual swale so it won't erode so quickly. If you need a deeper/steeper ditch due to space limitations or whatever it will be a little more tedious but do-able with your loader. I have used my loader to dig some pretty large holes and run some ditches in the past but it takes patience & practice on your loader to make a consistent ditch working perpendicular to it. Since your ditch is only about 3' or 4' wide on one side, it will be real tough getting in the ditch parallel and getting the proper angle of your bucket for digging, it will greatly widen the ditch in the long run.I'd just experiment some and see what works best for you.