First don't use the cork end gaskets just use a bead of rtv, also check the end rails on the block and make sure there are no dowel pins (aligning pins sticking out that are not allowing your intake to sit flush)
I noticed those dowel pins on my 73 when i did the manifold swap out. They just need to be plucked out because the new manifold isn't drilled for them. Pair of pliers is all you need!!