This is a common question and can cause lots of issues especially when purchasing headers and gaskets. Cast iron round port are true completely round ports while the Edelbrock round ports are similar to a “D” shape, this can be very confusing.
Take a look below to help identify your headers-
D-Port Headers look like two back to back D’s. Ports are very close together. Cast iron and Edelbrock have the same basic “D” shape.
Round port have completely round ports and separated farther out
Edelbrock round port has what you could call D’s but they are laying down
Good reason to know your port shape because the headers will not fit each other
