The bridge pickup cover on our Antiqtuiy P90 Soapbar has a long notch milled to fit over a flange in the baseplate.
We only do the milling, as well as the aging of the cover, by hand when we make a run of Antiquity P90 pickups.
We do not sell these covers as aftermarket items.
We do sell new P90 soapbar covers, which you can file or dremel a notch to fit on your Antiquity P90 Soapbar pickup. Seymour Duncan P90 Soapbar Cover