I used the Medice Manufacturing spacers on my 340 with both the iron heads and now with the aluminum heads. I started using them because I need more space over my 1.65 rocker arms while using the original style valve covers. I also found they fixed an oil leak that I was having after trying a handful of different valve cover gaskets. These spacers moved the valve cover up enough so that the gaskets (or sealing surface) were not setting in the oil puddle at the rear of the valve cover. They also gave my old valve covers something flat to seal against. Now I can use the cheapy cork gaskets with no leaks.

I did not paint my spacers but I have thought about it to make the spacers blend in a little more with the valve cover. But with the aluminum heads it would not have made as much of a difference than it would if I was still running the old iron heads.