I've heard that the ECU from the 300zxT is compatable or usable with the 280zxT....and that it makes the engine run faster/better because the 300zx...is a 3.0L...and the 280 is z 2.8L.....i dunno if this holds true...but only time will tell.
the computer is taken from the 300 and used in the 280, with the benifit of removing the afm and going to different sensor style, dunno exactly, never done it. Also the TB, which is bigger on the 300. The rear end, depending on what year it is, (I think it's 87) is a limited slip unit, good stuff. The front hubs are used in 5 bolt swaps, and you'd probably use the rotors (thicker, better) with toyota 4 piston caliper upgrade.