I really wonder if something like my treegetter might be easier, cheaper, & work faster. If your stumps are spaced out, where you only want to connect to one at a time, your implement could have only one V in it & be very simple to build. My tractor weighs only about 3500 lbs & we hang maybe an extra 1000 lb on the rear & it is amazing what it will pull. The link shows pulling trees, but we normally connect near ground level or just below. No hydraulics needed other than the lift & tilt of the loader. The closer it is to the tractor, the more lift and if designed right, the tilt can act as a leveraged pry bar against the ground. Also you can dig down to connect with more roots.
I presume your machine has hydrastatic drive. This helps a lot. We have seen times, on a hard to pull tree, we would rock back & forth with the rear wheels in the air, till the tree came loose.
here is a link to that thread.