sthurman ,the second photo is what Merckx were using on the Corsa Extra with under bb cabling at that time. I believe yours is actually this bb shell with the raised lugs ground off, I seem to see a faint witness mark in your photo of the bb shell on yours (see marked up photo). Likely it was done at the Merckx factory when the frame was made. Out of interest, have you a detail photo of the underside of the rear brake bridge?
