If you must abuse your tractor and need to add a ballast in the rear, you should keep the weight as low to the ground as possible.
Wondering why the attachment points of the weight couldn't be located to roughly a standard pattern.
Depending on the load, in some cases you need to have weight behind the rear tires to fully utilize the front end loader's capabilities. We have a tractor at work that has to have weight behind the back wheels or the front axle is overloaded when they lift the pusher box that is on the loader. The pusher box is within the loaders capabilities, but the front axle is overloaded if they pick up the pusher box. Aaron Z