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.
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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...