Here is a link to the 13th page of a series of photos of a PBY walkaround.
http://www.net-maquettes.com/picture..._id=13#afg-170
Look at the 9th picture, which shows a closeup of the blister. Note the edge of the blister shows two distinct rows of rivets. Your part seems to show three distinct rows of rivets where the supposed blister would be. Also, note that about 3 or 4 inches down from the blister edge is a flange that appears to run completely around the blister. Your part does not show the flange.
The 11th photo on this next link shows the "flange" more clearly but the two rows of rivets are rather dark in the photo.
http://www.net-maquettes.com/picture...e_id=9#afg-170