ok,

I just pulled the heads and had them redone, when putting things back together, (305 tbi stock motor by the way) I delivered the heads to the machine shop so I didn't clean the gaskets off. As a result I didn't know if I had the inserts or where they went so I didn't use them. After putting everything back together I see a used insert below the car. So I know they were there, but I didn't use them. Do I need them? what did they block off. I sure hope I don't have to tear the motor down again to put them in. Any ideas would help. thanks

 

The inserts limit of block off exhaust gasses from passing through the manifold to help warm the carb up when it's cold.

If your manifold doesn't have a crossover you don't need them.

If you need them, one side is usually blocked off and the other side is a restriction.