The 'E' Type Forum

I am preparing these exhaust manifolds for sending off to Jet Hot for coating and have found these markings on the back side. Wondering what they mean. These are from my spare engine; number RA 6419-9, which puts the build date in late 1964. Anyone know what is "inside" the diamond? And secondly, will the detail come out with sandblasting?

They are the foundry markings, and the casting date of August 1964 appears to correspond with the date of your engine. Afraid I cannot tell you who did the casting at that time - possibly Sankey or Brimar - actually, come to think of it I believe Brimar used a diamond logo