Thanks to those of you who have re[lied directly. The answer turns out to be something not indicated by an catalogs or manuals that I have. The name in the XK's catalog is a misnomer. The part id an extension of the Door Panel Finisher and is installed directly in front of the main finisher on the downward sloping edge of the door in front of the window.
Thanks again,
BobA
89 XJ40 Vanden Plas
72 E Type 2+2