anyone decode these wheels ? pic included

Is there a code next to the valve stem hole on the front side of the wheel?

My book does not show a wheel code of A. Could therre be another letter next to the A? I see a B code and a C code in my book, but not an A code. It may not be a Chevy wheel. My book shows Chevy wheel codes.

I see a number six in your picture behind the M. They may be from a 66.