Yup yup. They fit right on because they ARE 318 heads. They just have a more efficient combustion chamber. I have a fresh 318 sittin in the shop floor with magnum heads on it. Blueprinted it at 9.2:1. It has this little Voodoo Cam
http://www.summitracing.com/parts/lun-10200703/overview/make/dodge See the RPM range? 1800-6200. It'll make a 318 sound nasty, but still pull like a sumbitch because of its modern lobe design.
As far as the heads, the 302s are great for a factory iron head on a 318. Their 318 size ports make good velocity. Velocity, not port size is what's about. How fast you can get it in and out. Big port 360 heads on a 318 will kill it DEAD because the port size doesn't match the engine's ability to move air......unless you make a LOT of other expensive changes, such as bigger valves, more compression and so on. As I read this, I think you are after the best bang for the buck, not a money pit project.
302 castings though are lightweight, thin castings. Finding a good set can be problematic. Same with the Magnum heads......BUT when you find an uncracked set, you have something good. They will not crack unless subjected to abuse such as overheating or freeze cracking. The Magnum and 302s share about the same size combustion chamber......around 60cc and are capable of getting compression in an otherwise stock 318 short block to as high as 10.5 with milling, however, I advise against it, because with the stock 318 piston that sits in the hole around .080" at TDC, you'll have no quench and it will not be a pump gas motor. That's why I limited mine to 9.2. Yes, you can run more cam to bleed off cylinder pressure for more compression, but to me, that's a waste. Another thing to consider is, if you go with 302 heads, they share shaft mounted rockers with all the rest of the LA engines. Magnum heads require their own specific rockers and different length pushrods, since they were designed to run with roller camshafts.
Lastly, I don't know if you should look for "another" Comp cam or not. I don't know what you decided on. I wouldn't run Comp....unless it was their Mopar specific lobe cams, OR their Dual Energy series, such as the one I recommended earlier. However, if you go to the 302 or Magnum head, you can go up to the 275 Dual Energy, which is the next size up.
