First thing you must do is find a 280zx 82' - 84' turbo manifold, then get your block checked, if your block is stuffed, then go for a either L28 turbo or RB26DETT if you can spend the money, but if not just get the manifold, because it has almost very thing you need for the forced induction side, ok next your bottom end will need alot work though, will you go for the Turbo or Supercharger, thats the next question.
:bandit:
Don't be fooled the 1982 280zx GT race car had 588hp from a turbo, the lag wasn't really a major problem but when the car was under 2000 rpm there was a little lag(round town driving, but chuck on a anti-lag system I did only for the BackFIRE, hee hee hee).
:alien2: Turbo (you will need a BIG turbo, second hand you will be looking for at turbo of a 3 litre engine or bigger.)
Supercharger.
Above all go hard, I am still trying to find the layout prints, But I'll talk you through it, if need be.