That does not sound good news, at least you were quite near home.

If you look at the Vitesse Ltd web site the GB is shown without the extension part. So is the extension a non Mazda part? As Vitesse claim to be "partners" with Morgan did they make the extension?
https://www.vitesse-ltd.com/pages/about-us
https://www.vitesse-ltd.com/products/vitmgb251
Cheers
John