The Wells is an exact duplicate except there is no stamped Delco or part number on it. Only the original GM/Delco units have any words stamped on them at all. The more recent GM/Delco senders have nothing on them at all which leads me to believe that they have some outside manufacturer making them to some universal, one-sender-fits-all spec.
Here are two vintage Delcos on the left, then a correct old NOS Delco sender with the stampings and a more recent (inaccurate) Delco sender with no stamping, on the right:
Close up of some vintage Delco senders with the "AC MADE IN USA" stamping:
By the way, these are other peoples' photos - I don't have any of these senders. A Pontiac buddy just sent me the one that I tested and that one I put in the car.