Pinging on just a couple of conversation points. First, the longer the barrel, the greater the sight radius. Whether 4" is significant, perhaps "in the eye of the beholder". Pardon the inevitable pun! Yet, the sight radius as moving to a receiver from aft barrel sight, also its percentage of contribution. (Effect in handguns for me, really noticeable!)
The comment about original long barrels suffering "cut down", I suspect such was quite prevalent moving to 'more likely than not', probability. A rote generalization, but my perception that factors making 'long tom' factory orders themselves rare, also working similarly on the "second owner - et al" market. Where such as integral forged type front sights weren't involved, a 'pro job' typically easy and retaining 'factory original' appearance. The Great War, with Springfield orientation, sealing the deal. Viewing the hoards of cut down 30" barrel Krag rifles, by far the seeming majority existing today! My amateur thesis, over a century now of max 26" barrel popularity; past half century, max 24" or less, as 'almost' relegating longer to "highly individualized and often $$$ customs!
Yet 'hangin' for any barrel taper info available!
Best!
John
