In my opinion, the small "slits" head gaskets were designed for '72 and later blocks shown in the bottom picture as they enlarged the water passages. The top picture is pre '72 block, if you put a those small "slit" head gaskets there is about 1/4" exposed, the rest is entirely covered, I believe the larger rectangular opening on the head gasket you posted was designed for pre '72 block. I have spoken to Greg at Superformance before as he has the template for the original Mopar Connection steel shim head gaskets, and his new reproduction have the larger rectangular slots.

However, I have run both on '68 block and have had zero issues with either design.