What are all these holes for?

Also take a good GOOD look at the front/ rear mating surface, especially the front. Some manifolds "overhang" in such a way that they really don't seal. I NEVER use the front/ rear gaskets, I instead get everything "ready," lay a fairly large bead of (your choice color) I use black RTV, and then set the manifold down. Waste not time snugging the bolts down, and then inspect the "under" edges of the front area with a mirror, then take a towel/ your finger and smooth out the bead of RTV. Don't fire the engine for 24 hours if you can afford the time.