D6n is same size as a jd750 pretty much, it'll pull, amaze you how much fuel it'll pull too, and you'll probably only get 1 acre per hour. Get one that's just 1' wider than the machine. I've never seen a newer dozer with a mounted root plow. All the new ones around here go in a ripper. Holt top mount should be a good plow, expensive. Industrial Bucket in Dallas builds bottom mount plows pretty cheap, less clearance under the ripper bar for trash to flow. In Texas we plow through light trees and heavy brush, if you clear the land off pretty good I'm sure the bottom mount is fine.
Root plow brings all the roots to the surface, what looked pretty good to start with will be a mess after plowing, have to rake it again, still won't get everything.