Going to a 2-belt pully jus takes extra mass off of the front pully. It is comparable to putting in a light-weight flywheel, but much more easier. There is less metal for the engine to spin around so you get more hp to the wheels instead of throwing it into the third, unused pully.
Get a turbo AFM and change out the internals using a non-turbo. If you do this, be sure to get a larger throttle body, port the intake manifold to match the throttle body and do some polishing and/or porting on each intake runner. This all together will add HP as opposed to what some people say.
put on a 4.11 rear. If you havent' driven a car with lower gearing, then you dont' understand how much this helps. This is especially usefull for an 80 ZX. You will be going from a 3.54 to a 4.11:1 gearing. That alone can knock a half second off the quarter mile time if you are good with shifting.