Would the 1986 owners manual mention Dexron III? Unlikely, if GM first spec'd Dexron III for its vehicles in 1994...
All Z31 FSMs (and probably owners manuals) spec plain old "Dexron" for the auto tranny.
Whether there were any subsequent TSBs commenting on the applicability of Dexron II (B/C/D/E/whatever) or Dexron III, I can't say.
What Nissan has to say about the new Dexron-VI spec in our cars is anybody's guess.