Sorry didn't read this thread in its entirety ,  but  the Title made me remember, 
 My buddy Raphael just tore apart a Legacy 91' and has the front brakes available,  and i think between Ansel and I we have some rear calipers (older impreza)     .. Actually i have an other set of front impreza calipers (made for the 9.5" discs though ...         
  If any of that helps you out LMK ,  if not i'll keep em for rally spares.