I think before you do anything, you need to figure out what you have already!
Just buying an Edelbrock 600 and performer intake will not cure your ills if they aren't well matched to the cam and compression ratio.
So, you're dealing with a supposedly rebuilt engine that you know nothing about that apparently doesn't run very well. This could be for a whole host of reasons, anything from needing the timing adjusted all the way up to the previous owner lied about the "rebuild" which was really just a "repaint" of a 100k mile engine.
Figure out what carburator and intake are already on the car. Check the timing with a timing light to see where you're at. Check the compression. While you're checking the compression, take a good look at the spark plugs to see if the carb tuning is close (ie, black and sooty = rich , bright white and melty = lean). And since you've got the plugs out, make sure they're the right heat range too. A compression gauge and a spark plug socket won't set you back much cash, and a compression check is a good start to knowing you have a healthy engine. Throw in a timing light and a vacuum gauge, add a flathead screwdriver, and a 1/2" wrench and you can set your timing and tune your carb. It doesn't take a whole lot of tools!
If all of that sounded like gibberish, find a good mechanic that you trust and have them check all that stuff and do a complete tune up on the car. Otherwise, just bolting on parts may not do you any good. In fact, it could make your car run WORSE. Bolting a bunch of speed parts onto a worn out 318 with 7.5:1 compression won't help your cause, it will just cost you money. That may be a worst case, extreme scenario, but until you do a basic check of the engine, you don't know what you have. Better to spend $300 on some basic tools than $300 on a brand new carb you didn't need, or can't use...
