Think I read somewhere that the proportioning valves are the same on all of our cars. Whether its a Disk or a Drum....Impala or Caprice, all the same.
FWIW - I swapped my Drum Brake rear over to a Disk Rear and left the original PV. I picked up the Bolts to do this PV mod and have yet to do it. Getting to it this winter but may just go with a new MC with a builtin adjustable PV instead.