Well that looks like some sort of gearbox slid over the PTO shaft, with a hydraulic pump bolted to it? I think Archemedes said it best. "Give me a big enough lever and I will move the world" By the bent piece of allthread, it appears that you are trying to counter the torque of the free hanging gearbox with too short a lever arm. The short arm means higher forces which are exceeding the strength of the hardware you are using. Use a longer bracket, perhaps down to the backhoe sub frame or tractor drawbar.
It is hard to tell from the photo as I can't see much of the pump, but it looks similar to the ones that come with the factory backhoe. If you look right above where the PTO shaft, that you have hung that gearbox on, comes out of the tractor(behind the top of the PTO shield) there is, or should be a cover plate. If you remove that plate, you should see the end of a shaft with a slot in it. The factory BH pump has a shaft with a tab on the end of it protruding from the pump. Tab A is inserted into slot B and the pump is bolted to the back of the tractor using the same 4 bolts that held on the cover plate. That is how mine is installed...
