That S/N break could be somewhat helpful info to someone with a .454, contemplating purchasing or swapping grips from one to another. Again, bear in mind that there were .22's (252), .44's, and .357's (353) in production at that time with different prefix and S/N ranges.
Yes, I have examples of the bolt and nut attached mainspring originals, as well as examples of the slotted mainspring holder that came later. You don't feel the difference externally, but the difference in length etc., is obvious with the grips removed.
And, as I said, final individual fitting at the factory can still make for difficult grip swapping. The grips may or may not "bolt-up", but not necessarily "FIT".
Unfortunately, my photo posting skills on the site are non-existant.