273 "commando"

64 and 65 heads were #2532080 (casting number) and had the smaller intake bolts ant a different angle than the 66 and newer heads. The 66 heads were #2536178 early and #2658234 late (casting number) the 2658920 is listed as a 66-67 head and were used on very late 66 produced engines. All the 273 heads through 67 were closed chamber heads with 1.78/1.50 valves and advertised 57-64.5cc chambers.