What are you going to hang it on? I would think that it would be fairly straight forward if you just go from the picture. The spec shows 1400# plus 500# for the root ball, so expect 2000# total lift from one that size. Your mileage may vary.
It looks like the spades slide inside of a rail made from two "C"s face-to-face. The bar on top of the spade (inside the rail) looks as big as the cylinders, which he says are 3".
Of course, if I were building it I would hinge the side bar like they did but have the pin lock the two bars together around the front instead of just holding the one side like theirs does. It seems like it would be stronger that way, and you didn't "steal his design".
I'm not sure about the hydraulics either, but I don't really see why you couldn't put all three cylinders in series. Whichever one moves the easiest would get the pressure until it stopped, then another one would. Eventually they would all get fully extended. That way you just have one valve. His only has two hoses, so I suspect that's how it works.
Some of the more experienced builders can help with the hydraulics more than I can.
I think the real question is, how did that Christmas Tree get out in that field all by itself?
Good luck!
- Just Gary