It will make some, allowing the engine to "breathe" a little better. I would stay on the small side on the carb, 650 cfm, for a bone stock engine. Or you could find a spreadbore intake and run a well tuned Thermoquad on it.
For a carb, a 600 Holley or Carter will do well, or, a Thermoquad...if you can tune a carb.
On the intake manifold, there are a couple that come to mind starting with the old Edelbrock LD4B or the current Performer. Weiand makes the action plus which is also very nice. The LD4B needs a squarebore carb.
Regular street headers will do OK. There a real and true cursing pain in the back side event to do alone, so grab a freind and some TALL jack stands. No more than a 2-1/2 exhaust pipe, honestly, 2-1/4 will do for a stock 318 with bolt on's. Add a cam in the future? The 2-1/2 will do ya right.
