This fancy metal plate appears to be the warranty identification plate that you received after sending in the warranty registration card. What’s a little odd about this plate is that the MGB GT car plate number of 116543 doesn’t match the plate number of 116544. Interesting. I’ve attached the selling dealer page from the warranty book as well.
And yes, for you sharp eyed MGB fanatics out there, I did flip the plate in Photoshop so that it’s easier to read.