Cylinder head development in the 1960s was like an arms race. Chrysler reintroduced a bigger, badder Hemi, Chevrolet developed the big block with its canted valves, and Ford experimented with SOHC and Boss big blocks. Pontiac had its Ram Air line of performance V-8s, but the best of that bunch never truly got its moment to shine
Most Pontiac engines were limited by cylinder heads that used D-shaped exhaust ports, with the front and rear combustion chambers and their corresponding valves and ports mirrored in the middle, just like a small-block Chevy, Chrysler LA, Packard, or AMC V-8. This places the center two exhaust ports right next to each other, concentrating heat in the cylinder head and making exhaust routing difficult. In fact, some aftermarket headers use a single primary tube for the center pair of exhaust ports on some of these engine designs.
Read Brandan’s article here at Hagerty