Sony's jumbo box "Bruno Walter: the Complete Columbia Album Collection" consists of 77 CDs (8 of which are rehearsals, chat, etc.), and 9 of which are devoted to his American Mahler recordings for the label (1945-1960). All remastered by Meyer Media LLC, and b sharp music & media solutions. If you liked the Meyer Bernstein/Mahler box, this is worth a consideration. I got mine from Santa Claus.
I started with Andreas Meyer's work on BW's Mahler 2 (1958) and it's tremendous. Will audition the rest as time becomes available.
The remaining 50+ discs are good bonus material (Brahms, Mozart, Beethoven, etc.)