Deere used to make a toolbox bracket that bolted to the front in place of the starter weight bracket. My 5520 came that way and I still have the bracket. Maybe have a photo of it.
Mounting a proper tool box and then separately, a rock box is an idea whose time has come. I'm tired of being a long walk away and not having basic wrench or two. Even worse, to be doing field work and not have a place to put the errant rock. I shouldn't have to spend hours bending and welding a bracket to hold a box for a couple of rocks. There's not enough room on the platform of the tractor but that's where they go.