Jim
Look to see if you have a square plate with four holes in it welded to the axel just behind your spindle. These plates are what the backer plates bolt to. No plates, no
brakes you will have to replace the axel to get
brakes. With an 83 trailer you may be better off just replacing the axel if you want brakes. Backer plates, drums and bearings will be close in cost to a new axel.
Eddie