The round port idea was unique to the Crane heads. "In the day" , virtually ANYTHING you ground on the head made it better! Harvey knew the SBFord needed help so he began offering them. The round port is not "ideal" and racers soon figured that out so the idea never really "caught on". When Ford stopped producing the heads ( '68) Crane bought pallets of them and offered them until they ran out ( around '72). To work "properly" the header flange should be round as well and the only way to get that was custom headers "back then". They are still C5OE castings but are out performed by ANY aluminum aftermarket head even one from China. The technology is just that much better.
Randy