For what its worth I have the:
Mk28 part number L81252-10-03 as Ref No 6A/6669
Mk28B part number L81252-04-006 as Ref No 6A/1170854
Mk28C part number L81252-10-007 (and -009) as Ref No 6A/6379219
Mk28D part number L81252-04-008 as ref No 6A/6379200