I have been wanting to make a land plane too. But my grandpa said that why would I need it when i have a box blade, rear blade with gauge wheels, and a landscape rake? So I haven't made one, yet.
And if I did make one, weight is a must, kinda limiting since my little Yanmar can only lift about 500 pounds on the 3 point hitch. Now if i made one for the 3720 than I could make one real sturdy and heavy. I might even make it over built like all of the things i make and have stuff on it that aren't necessary but make it so it will last forever.