66 mustang engine ID, matching #'s?

How do you tell if your engine "matches" your car? There is a thin metal tag screwed onto the engine compartment side with all numerical information and numbers that match whats on the door plate. It is about 2 inches x 3 inches roughly and has a wvy sort of cut on at least one edge. All I have seen for number on the intake manifold are the firing order and some numbers just in front and a little to the left of the carb that dont match the door plate, but aklso dont seem to be the same amount of digits either. I have looked at a lot of pics online at engine compartments and have not seen this tag, thinking it may have been put there at some other time, but did it come off of the engine? Is this the engine ID? If not where do I look? All other tags I have found match (door, seats, engine compartment stamp in fender cut out, and that tag screwed into about the same place as the cut out but on the passenger side) I want to know if I can claim this car as matching #'s, if I go to sell it.

The tag on I think the driver side fender in the engine bay is right where it belongs. My '66 had it. Also most all original cars that you see at car shows have them. Its just another tag to identify parts by. I'm not sure what to tell you about the engine. What engine is it? That might help.

It looks original, I just want to make sure before I claim its "matching numbers" its the 289, 2bbl carb which fits the C code designation.