The Mexican Army adopted the .30-06 as standard after WW2, after they retired their 7x57 rifles & MGs.  Their M1954 (Mexican) Mausers were .30-06.  And I have quite a bit of FNM .30-06 brass.  Most of it is headstamped "FNM" and a 2-digit year, just like the US military stuff, and uses regular Boxer primers.  I think the "58" is just the year of manufacture.