[classical glass]

I have a 427 FE side oiler, just completed a complete upper rebuild. Valves guides
springs, seals, harden seats etc. everything was going great and smooth until it came time for the intake install. It doesn't want to seat perfect on the heads. There is a rocking motion hence something is keeping it from seating flat. I noticed the head gaskets are sticking out slightly from the top of the cylinder head.I had the manifold checked for flatness and straightness and everything is fine, so the problem is somewear else. Is it possible the lower portion of the manifold is just hitting the tops of that gasket? I'm installing a ford 2- 4 barrel intake which was the original intake that was on the car. I believe I seen somewhere that there were some tabs that needed to be bent because of this issue. Maybe not. Any input or help would be appreciated.
Thanks...