on my 91 4dr lx, i was doing some body work, and took the rear bumper off, then when i was putting it back on, the bracket that holds the bumper on, was rusted and fell off. i tried remounting it, but that didnt work. how do i reattach it? all inputs welcome

 

It sounds like it rusted through right where the mounting bolts were located (how else would it fall off by itself). You've three options:
1) Weld in new metal in the area rusted out on your original bumper bar and redrill it so that you can reinstall it.
2) Pick up one from a salvage yard and install it
or
3) Get one from Honda and install it.

there's not much else that can be done.

P