I don't think I've ever seen the full endurance package inside any N frame except .44s. Not even .41 Mag 657s have the "full meal deal" inside.[/QUOT
Around 1990 all N Frames have the improved lock-work, radius stud package, and longer cylinder stop notches. Even some 27-4s have it, sans longer stop notches.
From a production stand point, it is easier to make them all the same.
Read Supica & Nahas's first edition, denotes engineering changes to N Frames.
BUT, not the additional cylinder release block that requires milling a slot on the inside left side of the frame. I don't think the radius stud package was anything but an aborted attempt to make assembly easier for the folk on the production floor. (I have had need of the additional cylinder release block in a Model 58, which unlatched and partially opened multiple times in a "fun" IDPA match in which I was using full tilt factory .41 Magnum loads- just to see how crazy it would be in "the real world".... And as a lefty, pretty unlikely i was riding the latch!)
The longer cylinder stop notches do seem to have been incorporated across the N frame lines, probably for the reason you mention. (The purpose for those was to prevent the anti-clockwise rotation of the cylinder.)
BTW, I have 3 of the four editions of the SCSW, just not the newest one, so....I just like crawling around the guts of various S&Ws.