Most dimensions are shared by the standard and magnum length actions except, of course, length.
Even the distance between the screws coming up from the bottom metal is the same.
The foreward lug (under the receiver ring) on a standard action is out near the forward end of the action so the crossbolt behind it ends up more or less directly below the center of the front ring.
On a magnum action, the foreward lug is close to centered under the front ring so the crossbolt is farther rearward toward the back edge of the front ring.
I have been meaning to photograph this. It is very obvious in a side by side photo.