Okay, new and improved. I call this version "Mr. T" because of the shape
and because it lays trash-talking hickory trees out flat on the ground...
Still working with 2x3x1/8" box beam. I've got about four feet of height and width now with 1/4" gusset plates front and back. Added a grab slot for the chain on top.
Didn't have any problem with it falling over side to side during pulls, and soft soil wasn't a problem. Pull to get the chain tight and take out all the slack, then go back and adjust the chain position before pulling the tree. With the base near the tree for maximum leverage you don't get a lot of lift per pull. Smaller stuff comes out on the first pull, just pull the tool over and keep dragging. On larger stuff you might have to iterate a few times, but seeing the entire surface around the trunk lift out of the ground makes the time spent satisfying. The chain slot worked well, but I bent it trying something that I couldn't budge, so it needs to be beefed up.
I included a few pictures of test subjects, a couple different sized laurel oak stumps and a decent hickory. The hickory came out nice and clean, without a lot of devastation around it. The laurel oaks have spreading roots and require more clean-up afterwards, but it's still minimal compared to digging them out with the grapple. Pictures have a chunk of 4x4 in them for scale.
In addition to beefing up the chain slot, I'm going to use a thicker chain from the tree over the top because the mechanical advantage I'm getting applies to that part of the chain, too, not just what I'm pulling up. Also thinking of adding a rebar "hoop" over the top of the chain slot to wrap up anything headed upwards from the tree if something breaks.
-- Carl