I would think 3 max. Most magnum 98's as in .338's etc. only hold 3 3/4's. Thus the larger diameter .404 might sneak in 3 as well.
: The M70, 264WM I rebarreled to .458 Alaskan, then to .458 2", actually holds 5 standard magnums in the box. It held ony 3 1/2 of the .458 Alaskans which have almost identical case head size compared to the .404.