no, the "original" one piece bolts, all in the 'white' started at 1949 and the 'two piece did not appear until as I noted , the advent of the Korean War conflict and part of the "war effort" to save, not waste steel, Ruger went to the two piece bolt, little waste of materials, this was around 1953...YES, many years later, the Mk IIs did "try again" and use the the two piece method, but see they again went back to one piece design.........
the bolts are always in some 'flux" of changing, either to make cheaper, easier or to strengthen, make BETTER??
and over al these years these changes have occurred, as noted by the collectors and well pointed out in the Hiddleson Encyclopedia of Ruger Rimfire Semi Auto 1949-1992.................
another point if you look closely at the above picture the two different steels used in these bolts were quite different, , we often find (see) pitting in the 'flat' pieces and none in the round ( bar stock) I questioned if they used "used"??? steel................the flat pieces seem softer, and not as hard as the round stock ,could be in the 'heat treat' of the materials used...often if you come across one of these that was 'reblued" there will be a color difference in the finish, to me , its the hardness.............and again, they do "loosen" and may come apart!!