Intake manifold gasket installation help

-315 heads are for 64-65, 273s with small, 59-64.5 cc closed chambers. (Measure the volume to help you determine what compression ratio you will end up with). Those give a higher compression ratio than open chamber heads. The small, stock valves, 1.78 and 1.50, are light weight, which is good for higher RPM. Of course they had adjustable rocker arms to go with solid lifters too. Those are desirable heads. Small port 273 intake manifold gaskets can be more difficult to find but I think the 318 have the same size ports.
Dry fitting is important so make sure any gaskets used are held in place while doing that. This will enable you to see how big the gaps are and even to stick a feeler gauge in to measure them. Then you can decide which gaskets you need or even if some surfaces need to be milled.