Magnum length means it will feed a 375 H&H without modification. A standard M98 action won't do that, you have to remove metal from the feed ramp area of the action to cram that long cartridge in there.
There were some "Magnum 98" actions built by the Mauser corporation for export, and they were turned into very nice rifles by various British gun firms.
Generally a "super short" action is for the WSSM family. "Short Action" is for the 308 Win family. "Standard Action" is for the 30-06 family. "Intermediate action is specifically between "short" and "long" and the most common example would be a Yugo M98 action, specifically designed for the 8x57, although some of the small ring Mausers also fit the description. "Magnum action" are 375 H&H length (also 416 Rigby, 338 Lapua, etc).
Jimro