[markjohnson]

That rectangular port/open chamber #990 cylinder head was not around in 1969 or 70. That and the similar #188 are what came on the newer crate LS-6's and LS-7's. I've seen reference to this so-called cast iron ZL/X head and would like to know what the casting number is. The earliest cast iron rect. port/open chamber head I know about and have owned were 1971 dated #026. They are also listed in Colvin's book as standard issue for the 1971 LS-6 Chevelle. A car that never happened so they must have been over the counter service pieces. The 1971 Corvette LS-6 all used the aluminum rect. port/open chamber head #074, the same as found on the 1969 L-88 and ZL-1 Corvette.