Not a whole lot. Your EEC is controlled by SPEED DENSITY, which means that your engine's volume is preprogramed and set in your computer. Any changes to your engines volume will only confuse the computer.
I have heard of Guys swapping a Ford Lighting Cam into a 5.0 w/ noticable gains. Definately, Headers, and true dual exhaust w/high flow cats( let's keep the enviroment clean) will help. The biggest gain I have gotten was from a true cold air kit. Get some air into that engine, a 1"x3" hole hidden under the hood is not enough air for your engine. Maybe a custom chip, but none of these upgrades are under $200.
Much more than this, and you will need to convert to MASS AIR which requires a donor Mustang('88-'93), and some rewiring. There are some kits out there, but the ones I have seen still require you rob parts from a Mustang.
You will get more tips here that may help. GOOD LUCK