The 461 casting was used on Corvettes from 1961-1966; in '65-'66, it was the only head used on 327's - 300hp engines used them machined for 1.94/1.5 valves, and 350/365/375hp engines used them machined for 2.02/1.6 valves, with an unshrouding cut in the chamber wall adjacent to the intake valve. The same machining carried over later on the 462, 291, and 186 castings used with 2.02 valves.