I've had mine off before. I'm not sure what brackets you're talking about. From memory, there are brackets on the inside surface of the bumpers. These are connected (welded?) to the bumper. These bolt onto the body of the car. I don't know what brakets would be seperate.
For the back, just bolt them on. Put them on loosely, I believe there is some "wiggle room" to adjust them for level.
For the front, just bolt one side on then the other. Again, do it loosely so you can adjust them and get them to meet properly. Then put on the center cap.
Just dive in, it will make sense as you do it.
Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both tops
1994 E420