Carburetor upgrade and intake manifold

great conversation. I bought a '73 dart sport in july, slant 6-225. A few weeks later grabbed an offenhauser 4 bbl alum intake for $20, then found a holley 390 that requires me to rebuild it for $150. My plan is to gradually modify the engine( headers, dual exhaust, mild cam, new ignition,shaving the heads and maybe piston work)..I still want to drive her though. Can I add these things one at a time, will the car run with a 4 barrel carb but no exhaust work?..can I shave the heads without changing the cam?...I am not (obviously) making a race car, but want the car as stock as possible, but with a little pep and a nice growl.

if anyone can give me a ball park figure and specs on headers, a cam, how much to shave the heads, ignition and anything else they may have done , or other ideas, it would be greatly appreciated