18,000 orig. mile 318 build
First, get it running right, as mentioned here before. Check for engine fitness, and if it's OK, check if you have the lean burn system. If so, swap to a Mopar distributor with HEI module (or an older Mopar Performance P3690426 dizzy kit that doesn't have Chinese crap in it - can be had cheap on eBay if you play your cards right), first thing.
Consider 1992-93 Magnum exhaust manifolds instead of headers, if you can fit them in the F-body. (Don't forget to cap the air recirculating port on the passenger manifold - Stieger makes a $14 blockoff plate, and the gasket is available if you search around). They'll flow good and won't loosen up or cook your engine bay like headers (price will not be any better than new headers, unless you can dig them up in a junkyard). Either will require exhaust pipe mods. If you do the '92 manifolds, remember to get the Magnum-specific mounting bolts that go with it - the bolts at the ends of the manifold are longer than LA bolts (as opposed to the LA studs).
Edelbrock's Performer 318/360 often runs dirt cheap on eBay because it's ports favor the 318, not the 340 or 360 (ask me how I know). Thus, it favors your engine and pocketbook. The carb to fit it, on the other hand, will not be as priceworthy - unless you can find something local and lightly used. And remember, you'll have linkages that you'll have to fit onto the intake. Do some searching on Google at "site:forabodiesonly.com 4 barrel linkage" and "site:forbbodiesonly.com 4 barrel linkage" and you should be able to bring up some info about it (not really clear on it myself yet - not there yet with my 360 build).
That should make you pretty happy for now. Wait before you go cam crazy and tear apart the entire front of the engine apart to do so, because you'll pretty much force yourself into the cost of a double roller timing chain, water pump, water pump seals, break-in lube, an oil change, and general worry as you try to calculate the possibility that your expensive new cam just might inexplicably eat its own lobes during break in.
Incidentally, if I may backpedal on my own advice: The timing chain is highly advisable regardless of whether you swap the cam (you probably have a nylon gear set in there now), and Cloyes offers a $30 double-roller under the part number #C3028. Also consider Cloyes #95387 timing chain tensioner from the 3.9L v6 while you're at it - it replaces the cam thrust plate and is a cheap and good upgrade to stabilize timing. You'll also probably find that the factory did not put an oil slinger behind the timing chain either, and it should have one. Figure another $12-15 for one of those along with a new front seal for $5-8. Doesn't sound like much, but you'll be screaming at the overpriced little stuff more than the expensive big stuff by the time you get here.
It adds up.
-Kurt