Of course there's no headers available for those either so you would have to make your own. I assume that is a standard D-4/D-6 port and bolt arrangement. They used to sell exhaust gaskets for those but I haven't seen any in forever. Those water passages are so small the guy that told you they were 1/2 water heads might have been correct. Especially since KB was a Top Fuel shop. They might have been made that way for strength. In the mid 70's the supply of aluminum hemi heads was drying up. The Ross Foundry heads, aka 433 heads, aka replacement heads, aka twin plug heads were the only thing they had. I don't know if Chrysler even had any left. The D-6 castings were so bad I never saw one on a Top Fuel car. All of Chryslers R&D at the time was based around the D-6 port head. And I don't know if they even used them. I think all their R&D heads were 433's turned in to D-6's by Mullins. I think Chrysler knew they needed new heads and I'm sure KB knew he needed new and stronger heads for his engines. At the time Chrysler and KB were in bed together. All 426 Hemi R&D at this time was done at KB's. KB knew the D-4/D-6 port looked the best so he got the patterns from Chrysler and the KB head was born. Still the best looking 426 Hemi ports. I have no idea what the idea of the rectangle port like mine is about.