[rotorwrench]

The numbers on the heads usually begin with C in Canadian production. In the 8BA era, they generally follow the standard Ford prefix number/letter coding with the exception of the C at the beginning. They did make aluminum heads in that era too but they were generally special purpose items. A person also has to check the suffix. "AS" was a Ford suffix for special purpose items like the Denver high compression type heads. A lot of the Police Package engines used them.

In the US, the 1CM heads were a replacement for the older 8CM parts for Mercury cars. In 1952, they changed to the EAC prefix for the Mercury. All Mercury heads had a reduction in the chamber volume to make the increase of cubic inch displacement balance out to the same compression ratio as the 8BA Ford engines. Ford didn't take any chances on compression ratios due to the wide variation of fuel quality at the time even though it was getting better than it was before the war.

PS Chamber volume was Increased not Decreased for the Mercury per post 5. Brain Fart! The reduction was in compression ratio to match the Ford 239. Good catch.