There are two C7ZA exhaust tips listed in an MPC dated August 67. The star symbol is for "Aluminized or Aluminized and Stainless Steel". The @ symbol is for "Stainless Steel". Of course, the material is referring to the service part - does not guarantee the original part was the same material. Based on the usage charts it appears the -A was dual tip, and the -B was single tip. I don't know if this helps the discussion - it's just some data I found that appears relevant.