That hyd scissor lift in your picture is not meant for semi trl dump, won't have the power to lift a full box of dirt. That's designed more for a trk box scale length of 14 or 15 foot.
I think it's Lesu that offers a decent 4 stage hydraulic telescope cylinder that might stroke long enough for that box length, cyl would connect to the front of box. And I think they have screw drive too, the same one I'm using on the same trl in your picture. The Lesu website must be new & under construction b/c I can't see anything past their opening page & the search gives a blank page.
This link takes you to one Lesu's trk kits showing the hyd telescope within a serires of pics, it's all I can get to work on their site. The description says 5 stage, but that includes the bottom barrel that holds the extending 4 barrels.
https://www.rclesu.com/index.php?c=c...&a=show&id=444