well it depends on what you want to do with it!
Pro-Drag throw a nice 302 or 305.
Street 13bTt or Tri-rotor
casual every day 626 engine is perfect
if you decide to go rotor be prepared to be an on the spot mechanic and take care of the car like an infant. Means little to no drive and park driving mind you it is a converted airplane engine so it is built for the longer drives. I own an 85 RX-7 with the 13b in it and the previous owner tore it up now it is getting a complete overhaul. I cannot decide weither i sould throw a 305 or go for a jza80 or AE86. Dreams!