A parker "D" grade 16ga. stamped on barrels Sleeved and above that "WESTLEY RICHARDS". Barrels are 27 3/4". Ser# 74890 with a 3 over it and the D under it on the water table. What is the 3 and did Westley Richards do the sleeving? Or is it just a set of there barrels on this gun?

Thanks

Tommy (Again)