If you happen to have an intake w/ the heat crossover passage underneath the plenum, it won't fit b/c it'll hit the valley plate. The valley plate goes straight across unlike the factory valley pan gasket which droops down under the manifold to give clearance.

Example...a Holley street dominator manifold won't fit unless you mill down the crossover. I know 99% of the people running Indy heads don't use a manifold like this, but letting you know just in case.