On factory 340 intake manifolds: what are the two plug looking fittings in the bottom for? I took off my carb and saw them there; can they be removed? thanks 
Exhaust Gas Recirculation (EGR)
On 340 and 400-4V engines, exhaust gasses enter the intake manifold through orifices in two jets in the crossover passage below the carburetor. After 12,000 miles of operation inspect the floor jets for deposit buildup. With engine off and carburetor air cleaner removed, hold choke and throttle valves open. Using a flashlight inspect the floor jets visually through the carburetor. Condition is satisfactory if passage in jet shows open path through the orifice. If jet is plugged, remove jet, clean and reinstall. Inspect and repeat service every 12,000 miles.
Back in 1973 after I had my car for about 3 months, I removed the floor jets and I soldered the orifice closed. I then reinstalled the floor jets and I have never looked back.
If you remove them, you need to put them back in....so, either clean them or close them off like I did. Do not drop them into the engine if the manifold is on the engine.
