Per the Winchester records at the Cody Firearms Museum:
Win. 1885, SN 49xxx
Serial number applied: 5-27-1891
Date into warehouse: 6-18-1891
Type: Rifle
Caliber: 38/56
Barrel: Octagon
Weight: #3
Length: 28 inches
Trigger: Plain
Date shipped: 6-18-1891
Order: 6030

So, the barrel was changed to a Winchester #3 barrel, 30", chambered in 32/40 at some point. Based on the condition of the barrel, am guessing it was long ago. I bought it anyway and will pass along to someone who will treat it right. Since it came out my local gunshop, I was afraid that someone would pick it up that would not appreciate its history or what it is. I'll likely keep that sight for my Marlin 1894 in 25-20, which I will be restoring over the next couple of years.