Fox,
Thanks- didn't know that, and now I do-- so if I use this 70-S Buehler base, the front most D&T'd receiver ring hole is "plugged
No, that is not correct. The base is mounted using both factory drilled & tapped holes in the receiver ring & the rear of the base base should line up with one of the holes in the receiver bridge. If it doesn't I'm not sure what base you need.
There were a few very early post war M70 rifles referred to as "transition period" that still had some features of the pre war rifle & did not have the receiver bridge drilled & tapped from the factory. Normally the bridge would be gunsmith drilled & tapped for the pre war base. In a Buehler one piece base it would be a # 54.
I hope this helps.
BTW: to avoid confusing anyone, I previously referred to the long M 70 Buehler base that places the front ring farther forward as a 70 L but the actual Buehler # is 70 & again the shorter base that places the front ring farther to the rear is the 70 S. Mounting hole spacing is the same for both bases.