I see an issue with it not being triangulated enough. You have more of a trapezoid, not a triangle, so its going to want to do what a cardboard box with no ends does- flatten. There is 1 weld to stop it, but a lot of force is going to be put on that weld. In the pic below I circled the weak spots in blue. I would start by welding up the lower rear bolt location to keep it from being so easy to pivot (the rearward spot I have circled in blue), then weld in braces to strengthen it more. I would do one of two things- either weld in a brace running what I have marked in red, or use something like 1/4" plate to make braces to weld in where I have marked in green. You might even be able to leave the bolts in place if you go with the plates (green) but I would feel better if that bolt location was welded up.
Just a thought. Otherwise it looks good, I'd like to put a plow on when I can get a Deuce to keep for myself.
Jim