According to the Owner’s Manual, the engine number, which is the last eight numbers of the entire VIN, is stamped on the engine block, transmission, frame, and transfer case (if equipped). Doesn’t say specifically where on the frame it is located, and I’ve never seen it on mine. Seems odd that the Spanish authorities require a stamping that is only a partial VIN, but it’s their country so they call the shots. Some websites suggest the frame, above the wheel, is a common location, but they don’t specify which wheel.
As a Ford Motor Company representative I had to oversee replacement of windshield VIN plates several times, and the process was handled with more security than you can imagine. VIN plates were treated like first-born children.
Sorry I can’t offer anything more.