I had pioneer equipment fabricate a dump cart axle with 4′ steel wheels around 6 years ago. I like it a lot. I use it with a pole and a team of oxen. For the oxen you want the body balanced forward of center around 6″. This keeps the weight from pulling up on their yokes and choking them. Even with a 2000lb load their really isn’t too much weight on the pole, just enough to keep it pushing down.
Also I just bought a $250 poly dump from DR Power that is around the size of two wheelbarrows. It has a tractor hitch. I haven’t used it yet but it seems rugged. It is made by Ohio Steel.