I'm not a GMC guy but I did look around and did not find a 1951 GMC 250 with a hood ornament. That feature on the underside of the hood, my 1954 3604 has the same feature and I'm fairly certain it not for use for the hood ornament as it mounts much further forward on the hood and mounts over the center strip. There may be a "parts & accessories " book for the 1951 that may list (if available) hood ornaments as an accessory. That would provide a GMC part number for the ornament if there is one.

Ron - - Dusty53
1954 Chevy 3604
In the Gallery Forum
"You can't dance with the Devil and then wonder why you're still in Hell."
"They will forget what you've said, and they will forget what you have done but they will never forget the way you made them feel."