edelbrock heads on a 318

The Edelbrock heads are better than most any iron production heads (W2 would be an exception), but they would probably be overkill for your setup.

When you say you never changed the pistons, do you mean you are still running the original pistons/bores? If this is the case, and you wish to raise compression and/or make more power, that's where you should spend your money.

Now, if your current heads are shot and you have a stack of cash burning a hole in your pocket then by all means buy the small chamber Eddys. BUT don't expect a whole lot unless you change pistons as well (KB 167s would be a reasonable choice). And you'll certainly want a Performer RPM manifold to get the most out of the heads.