Here is some pointers on it not knowing the year,tranny and rear gear under it. Please inform us on the complete car for specific details:
Dont start putting performance parts on a Z28. Fix the flex problem first. Install larger tires, frame connectors, and a tower brace before any major engine mods. These cars have lots of flex under harsh take offs. Fix this problem, without any engine mods expect quicker ET's with less body flex. No joke. The car will pull harder off the line. First mod. I recommend on any car berfore the engine is tore apart is free flowing the exhaust and intake more. Open the airbox up with a free flowing air filter like K&N or others. Go with headers and a nice muffler. This will give you some seat of the pant HP. Nothing major but some. For a harder launch, install a stall converter. Dont go with a huge one with a stock cam but a 2200 would give you plenty of lauch if the car is an automatic that is. You never mentioned that. Put a larger gear in the rear. This will improve pulling power. You can do lots of things to the car to make it faster and handle better. Get the power to the ground. Dont have a car that will smoke the tires off the line. Have a car that will pull the front tire off the ground if you know what I mean.
You can increase ET's by not even messing with the engine compartment. Get rid of flex and increase ET's. Go with a larger gear and get rid of the Economy gear in it. The gear that is installed in most cars are made for less fuel consupstion. Get rid of it.