What rear ends fit a 69 el camino?

Your El Camino is an GM A body so any 68-72 GM A body rear,10 or 12 bolt, will work. Chevelle, Monte Carlo, Cutlass, Lemans, Skylark, El Camino or GMC version, or the muscle car version of one of these will work. 66-67 A body is about 1 inch narrower but will also work with some thought on wheel/tire sizes. New Ford 9 inch or Chevy 12 bolt are being made. A Google search will find many offers for them.