Here are some possibilities:
Ivory White
PPG/Ditzler 8177
Dupont Lucite 8207L
Dupont Dulux 97111
Old English White #1
Dupont Dulux 83445
Maybe useful, maybe not: Rinshed-Mason paint equivalent to BMC code from an old factory Tech Service Bulletin
R-M Permax 2U5599R
R-M Lacquer U9938 (good luck finding these).
All of the above are BMC code WT3.
To the best of my knowledge, Old English White and Ivory White are the same color. For earlier cars, the name of the color was Old English White. For BJ8s, it is Ivory White.