I'm working on a 1983 Dodge truck with a 318. I want to change the intake but the the intake flange will not seal the "eyebrow" portion of the passage way on the head. They look similar to 302 castings but I'm not sure what they are. Do I need a special intake?

that U shaped passage in the middle of each heads' intake face, you absolutely want it to be open

What are they for? Where do they go?

they are "air" barriers to keep the heat riser heated air that flows up in the roundish port in the middle of the "U" that goes across/into/under the bottom of the intake to heat the cool AF mixture, from overheating the 2 ex valves that are on either side of the U (those paired valves are too hot the way it is). EDIT No intake blocks those passages

What keeps them from getting filled with crap? The stock (EGR) manifold had a passage to cover them.

(1) nothing really, generally not enough debris makes its way up there. (2) Yeah you are correct, an EGR mani would cover em as it lets some of the ex gas in question (from the center roundish port) back into the intake (Exhaust Gas Recirculation)

You keeping the engine clean.

If the engine gets covered in debris that will not burn up from exhaust heat then it will fill up with crap ...

I thought that's what they were for, to collect crap. Never seen a clean one on a running car.

R.