At nauseum..318 intake manifold to 340 or 360.

I find it unlikely that a two barrel intake would be installed on 340 heads. You may want to take a valve cover off and look at the part number on the head and post back the number so we can tell you what kind of head you have on your 318. The 318 intake manifolds have smaller ports than the 340 intakes. It’s important to put the right intake on the right head or you’ll get a port mismatch and the motor won’t run as good as it should.