Here are a couple of more pictures of the Hall header.
The port is round. They do not step down.
The picture that you posted is of the Pat Michal header. They're nice but they are $1,200.
If you are going to worry about the header port matching the head of the 4v iron head, then you expect too much out of the head and just go for aftermarket aluminum ones with raised ports.
The exhaust port on the original 4v head is not optimum at all.
You CAN get the iron heads to "work" but particularly on the exhaust side, you need radical modifications to it.
I think in this case, it isn't necessarily the shape of the port that is an issue, it's the size of the tubes. 2" primaries are what you want and something like 34-36" long.
