Simple Easy Upgrades

It's not as "glamorous", but you'd get way more bang for your buck by milling the cylinder head to raise compression and swapping to a better gear set out back.

If you're more concerned with impressing people when you pop the hood, then by all means add a set of headers and a carb/intake to an otherwise stock engine. It won't hurt anything, but it won't make things too much better, either. Stock slants have VERY low compression (7-8:1). Unless you deal with that first, you probably won't be satisfied with the results.

You don't need to rebuild the engine to get real improvements, but bolt-ons aren't the way to go for substantial results, either. They're just easier.