273 Exhaust manifold
My 65, built in December '64 had the split set. The upper was on the car when dad bought it in '75.
This set I pulled of a 66 formula S in the junkyard in 2003, had the over the hump.
Really have no idea what the actual difference in years and part numbers were.
When I worked at checker auto in 1990, they only had the over the hump version...