If it was me, I would get a set of magnum heads for that 318. The thing is, you could probably call up LKQ and pick up a 360 magnum that could work with the proper flexplate. Already has the magnum heads and more inches too. Get a magnum style intake manifold and use your existing distributor and away you go. You'll have a hydraulic roller setup too. Cams are a little more expensive, but if the motor is good, you can reuse the lifters.