My thanks to those who responded to my query on- and off-list. The unanimous response was to apply code "e" (Earlier established form of heading (national authority file)) to the 400 $w/2 slot when flipping AACR2-compatible (Rules: "d") records to RDA.
Mark K. Ehlert O'Shaughnessy-Frey Library
Cataloging and Metadata University of St. Thomas
Librarian 2115 Summit Avenue
Phone: 651-962-5488 St. Paul, MN 55105
"Experience is by industry achieved // And perfected by
the swift course of time"--Shakespeare, "Two Gentlemen of
Verona," Act I, Scene iii