If you are using the factory intake, then yes you have to use the vally pan seal. Use RTV on the front and back cross seals (rubber) where they meet/mate up with up with the heads. I also put a small amount od RTV around the first and last ports of the heads as I believe theses are water passages that are not used. If you're using and aluminum intake manifold, then you need to use a paper intake gasket and on the front and rear of the block web (where the rubber strips would normally go), you'll lay down a thick bead (1/4") of RTV to seal. Torque all intake bolts according to the manual.
I use the valley pan on an aluminum intake as well. The whole purpose of the valley pan is to keep hot oil from getting on the bottom side of the intake. The small gap between head and intake is normal and the aluminum will seal in place when torqued. I also use the rubber strips with a small gob of silicne in each of the corners where rubber meets the head.