Small block Mopar cylinder heads can be divided into 2 broad categories (I'm ignoring the later Magnum heads) - small port (for the 273 and 318) and large port (for the 340 and 360). The small port heads also come with small valves (1.78" intake and 1.50" exhaust) and only flow about 135 cfm on the intake side. Compared to the even the worst large port heads (which flow around 190 cfm in stock form), this is quite a performance hit. Because of that, most people building a 318 for high performance just throw away the stock heads and substitute the larger 340/360 heads. When planning my 318, I decided on a different path.
The problem with running the large port heads on a 318 is that the larger ports, while giving greater flow, do so at a lower velocity. On a smaller engine, this can have a bad effect on low end throttle response. If there was a way to get higher flow through the small ports, top end power could be greatly improved without giving up intake velocity and low end throttle response. In fact, there is a way. Hot Rod Magazine has an article available on line that explains how to modify a set of 318 "302" castings for better flow. They also did an earlier 318 build up using the same heads but without enlarging the intake ports to match a 340 style intake manifold. These are the heads I've decided to use on my 318. I believe they will equal the 340/360 heads in top end power, but give me better fuel economy and low end throttle response. I should have my engine back and in the car in about 5 or 6 weeks, so I'll find out soon if I'm happy with the performance.