Hello Tom,
Thank you for your efforts. Yes, I do think it a factory replacement. Why they didn't do the Sousa checkering is anybody's guess. Mine would be that is what the customer wanted. I plan to dig up a Sousa photo similar to the CU of the receiver and post it next to your gun for comparison sake. I think it will be very similar. Glad the duck turned to gold! Can you re-send a photo and I will post it??

Walter c. Snyder