heads
Look, those things are nearly 40 years old, can you say worn out? On top of that they are old technology, and they don't have hardened seats for unleaded. How much money are you going to spend on them? And for what? You could buy new castings and spend a little to clean the ports up and have an all around better performing head with years of life left in it for about the same money. It's a no brainer, same money, better performance, what's not to like?
I've got W5's on my car, they aren't considered new technology either but they are light years ahead of those old iron castings.