In order to try to help the OP, I went to reasearch of my own, through my collection of Gun Digest magazines, since number 1 (1944) till edition as of 1963.
However, my reasearch was all in vain.
Have no positive result on winchester m70, in 9.3x64.
In GD edition, 1963, which is the last to have a chance (for pre 64 win m70), below is the list of calibers, per each contemporary american made rifle. (Winchester, Browning, Remington, etc)
Lack of european metric chamberings in American contemporary factory made rifle is evident. 9.3x64 not available.
For example, win m70 in 1963, was available in: 220 swift, 243 win, 264 win, 270 win, 308 win, 30-06, 300 HH, 338 win, 358, 375 HH, 458 win mag.
In similar way, although same table is not given in all eariler magazine editions, I could not trace 9.3x64, in earlier production GD catalogues.
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