i was told if i replace the heads from my 82 and put in some from an older model that it would juice up the power a little

 

Sure, you could do that.
There are threads on it that will really help you out.
Do some searches, and see what you can find. You can find more than we can remember to post again.

 

add some flat tops for more juice

 

Is your 280zx a turbo or n/a? How much power do you want? How much money do you want to spend? How much work do you want to do?

Indeed... doing research helps. Taking your head to a machine shop is usually (all around) easier.

 

search p79 or p90 decking .080"