As suggested above, "tapered" rifle slings are available in considerably greater width than the associated "bases". In terms of "affecting originality", first question whether the specimen is yet original & relatively pristine. If not, non-issue! Believe too, aftermarket pre '64 Model 70 repro sling bases are available as proximate copy... to have one's way with as preserving originals. The separate as 'last shoe' question, whether the sling configuration binding barrel to stock and beyond, is of such feature-condemned consequence in accuracy impinging concern.
I have my small cluster of collector pre '64 specimens and my "user friendly" field several. Common '06 chambered Standard Models showing field wear & tear. I'd replace those swivels if convenience/ergonomic comfort concerns. Just not to "F" with a yet original stock often defined as "recoil pad installation, as terminal modification!
Just some considerations and alternatives reflecting...
My take!
Best!
John
