The almost identical sight might have been an A. J. Parker, which bears a strong resemblance to the Ross sights made by Cooey and Canadaicon Tool. I believe it was fitted to early Mk II** rifles, and the Ross battle sights are a modification of that design. There are subtle differences. It would be interesting to know if the OP's sight is the standard battle sight or the target version with the smaller aperture. the finger grooves on the windage adjuster of the target version are in three sections while they are in one continuous section on the standard battle sight.

I believe stamped bridge in the link is referred to as an Armstrong bridge and was the first bridge with charger guides. The milled version in the link, and the OP's, replaced the stamped version.