Fox,

The S (short) designation on the Buehler 70S base refers to where the front ring is located & has nothing to do with which action it was intended for.

The 70L base & 70S one piece bases have exactly the same hole spacing but the base is longer & moves the front ring about 0.8" farther forward to accommodate the turret position of a longer scope.

Either the 70S or the 70L will fit on a post war(non magnum length, ie. 300 or 375 H&H) M70 Winchester action that was factory drilled & tapped. In Post war Pre 64 M70's you only had the std. action & the magnum action.

Any chance your M70 Swift is built on a pre war M70 action or very early transitional post war action? If so it requires a different base for the prewar style action.