When Winchester designed the Mdl 70 Classic long action they made the action long enough to accomodate a .375 H&H round. This resulted in an action that was around 3/16" longer than the pre-64 actions. Thus the classic long actions do not have to have all the extra machining to accomodiate the full length magnum rounds.
I'm in the process of converting a classic stainless orginally in .300 Win Mag into a .375 H&H and wonder what mods Winchester did to make a .375 rifle. I've opened up the magazine box by removing the spacer and removed the stop off the bolt collar already - these were obvious differences. I used a factory .375 H&H barrel and stock so those parts were easy also. The ejector may also be different; I've got to look at it closer.
Any anyone help me out with any other modifications I need to make? I don't have an orginal classic .375 H&H rifle to compare to so I'm a bit lost as to everything else I need to do.