Eddy heads - will I feel a difference on my 340 ?

Let me say this, there is a lot of misinformation bandied about. This is what I know for a fact.

Any aluminum head needs work out of the box.

Aluminum heads offer a greater potential, not necessarily better performance out of the box.

Aluminum heads are lighter, my car lost 40 pounds off the front end.

Aluminum heads are repairable, you should never have to replace them.

Aluminum heads dissipate heat much faster than iron. This is why some people believe they need 1 point more of compression than iron heads do. I dare anyone to prove this.

So, unless this is strictly a street car and the budget is limited I would recommend aluminum heads. You'll need to research them though and chose the best ones that you think will match your car's intended future use.

My motto is save the money and buy the best suited parts the first time. It's cheaper in the long run.

I resisted aluminum heads for a long time but after I made the switch (small chamber W5s for me) I'll never, and I really mean never, go back to iron. And I had W2s. There was that much of a difference in performance and weight for me. No question, aluminum is the only way to go if you want to get the most from your engine.