Update
Skinner Winged/Tactical sight for Henry Big Boy Steel is a Go
As mentioned above, I was interested in a winged sight for this gun and found that RPP is currently the only manufacturer to offer this. However, I contacted RPP to find out that their sight is of proprietary design inasmuch as the only apertures that work with the sight are theirs, whereas I wanted the ability to use different apertures of standard threading, which Skinner allows. The problem is that Skinner doesn't list a winged sight for the Henry Big Boy Steel at their site. Thus, for a short while I was stumped. Until...
I did some research online and found that others have discovered that sights for Marlin's 336 rifles are of the same hole spacing found atop the Henry BBS receiver. The problem is that due to the
location of the pair of holes, which are located further forward than on the Henry, Marlin sights overhang the rear of the Henry receiver, placing the sight too near the hammer. Photos illustrate:
Henry BBS receiver:
Marlin 336 (at top):
But what about that rifle below the 336? Those appear to be of the same spacing and very close to the same location of those on the Henry. Well, it's a Marlin 1894. Confirming the 336 and 1894 share the same spacing, with only the location differing, I went back to Skinner and found they offer their Winged/Tactical Sight for the Marlin 1894. Got it today and it fits the Henry BBS perfectly. So, even though Skinner doesn't currently list the sight for the Henry, I can confirm the Marlin 1894 sight does indeed fit and work.
In other words, the factory drilled and tapped rearmost scope mounting holes location and spacing on the Marlin 1894 and Henry Big Boy Steel receivers is virtually identical, including the thread size/pitch. Skinner's Marlin 1894 Winged/Tactical Sight on my Henry Big Boy Steel Carbine .357:
The great thing about this is the Skinner sight is a nice heavy duty unit, it offers great adjustability, provides 5 additional inches of sight radius and allows for the use of standard thread apertures of your choice. Not only that, unlike most other options, it sits low enough on the receiver to where it works with the factory front sight, co-witnessing the factory buckhorn sight on the barrel perfectly.
So, now owners of these newer Henrys have a previously unknown option for peep sights.