That depends on how much work you want to go to and how much you want to modify the rifle. The obvious choices are the 338, 375, and 416 Whispers all of which are made by necking up a 7mm BR which has the same head an body diameter as the 30-06. (they can be made by cutting and necking down 308 or 30-06, but with more difficulty).
Of the three only the 338 or 375 have enough shoulder to headspace the cartridge. while the 416 headspace on the rim. The 3.34" magazine of a 30-06 Win 70 should be long enough to work with the heaviest bullets for any of them. So that's just a rebarrel job but you still need to find a source for a chamber reamer and loading dies. Is there some reason you want it to be a "Whisper" design? The Whisper name is proprietary to SSK.
http://sskindustries.com/ar-10
Threaded Mode