Let me add a little info to your quetion.

I recently installed an Edelbrock Performer intake manifold on the AMC 360 engine in my CJ7. It sealed up the first time, with no fitment or leaking problems. The procedure called for me to remove the heat shield from under the original cast iron intake manifold and to rivet that heat shield to the bottom of the Edelbrock manifold, with the provided fasteners. I did that.

The ONLY gasket that I used was a FelPro metal valley pan gasket. I followed the instructions and used a very small amount of RTV (the copper hi-temp kind) around the head junctions. A small amount of black RTV was used at the forward and rear areas, IAW the instructions. After it was buttoned up, and the 4150 Holley Truck Avenger carburetor installed, I waited 2 days, and then started the engine. Performed oil leak and vacuum check -- no leaks. Engine pulls 19 in. of vacuum at idle.

Here is something you may not know. On the FelPro valley pan gaskets (and possibly on other brands), there is a pressed-in "ridge" around the intake ports. When the intake manifold is tightened down IAW instructions, those "ridges" act like a soft crush washer. That enhances the seal between the intake manifold and the heads.

For that reason, many mechanics do not like to re-use the metal valley pan gaskets, even on the same engine. If re-used, the amount of "crush" may not be the same, and that may facillate leaking.

Good luck.