Looking at it from the POV of the rifle, there is sufficient Clearance between Mag.Well walls and the sides of the clip, definitely for .30/06, and also for the 0,005-0,010 difference in Shoulder diameter between 7,62 and .30 cal…the Clip Expansion is even less of a “problem” as the diff. in case diameters must be measured at the Point of the 7,62’s Shoulder, NOT the .30 cal. which is further forward.
The Bases, as mentioned, are more of less Identical, so the Clip Base (the “heaviest” Part) is the same.
In any case, all the countries which used “re-chambered” M1 Rifles (Set-back barrels or New Barrels --Italy etc.) did not change the clip dimensions at all, NOR changed the Internal Mag Well dimensions AT ALL.
Another Point is that the US Navy uses a different designation system to the US Army & Air Force…The Navy uses an “M plus Mark” system. Just to keep us all confused.
And the USN simply converted the M1 rifles by fitting a Chamber reducer ( Firmly pressed in place, and then, Reamed the remaining chamber to allow for the larger diameter Shoulder of the 7,62 case compared to the .30 case Diameter at the same Point. So if you lose the “Insert”, a subsequent .30/06 case will fire, but have a "double shoulder ( ever so slight). A 7,62 will still chamber and fire, but will come out a straight (slight shoulder) .45 cal. case!!! ( Just like mistakenly firing 7,62 in a unconvewrtyed .30 cal chamber (perfectly tapered case, with a slight mouth roll over where the 7,62 case reaches the beginning of the 30 cal shoulder and the shoulder and neck have blown out of the 7,62 case.
All very nice "Theoretical “Musings,” but of no Practical consequences for Clip supply.