4.3 what?

The stock differential on a 5-SPEED is 3.27. the 4.30 differential is a shorter gear. It will anable you to get through the powerband a hell of a lot quicker than stock. I have 3.73's and @ 70mph my RPM is @ 2400, where as stock it used to be 2000 RPM. You will lose a little top speed, but you will get there a lot quicker.

If you get springs you are going to need new shocks and struts, I recomend the Mach 1 shock/strut combo, It's only $160. I went with Ford B springs and the shocks/struts and the total came to a hair over $300, only $80 more than Eibach springs alone. If you want more info just PM me and I'll tell you where you can get them cheap.

Also, get gears as your first mod. Most that didn't (me) wish they did it in the beginning. With a 5 speed I'd go with 4.10s or if it's a daily driver 3.90s. It will raise your highway rpms a bit, but knock off 3 or more tenths in the quarter. About the only mod as cost effective as gears is nitrous.

Just read up and do alot of searches on the forum and figure out what you are looking for out of your car.

And once you start modding you'll never stop, I need a damn 12 step program