That is quite the unique shotgun. Perhaps it was ordered by a Pigeon shooter that didn't like the rib extension in the way for loading. Quite a few Parker Bros. were ordered without the rib extension.
The late Charles Semmer in his book
Remington Double Shotguns certainly didn't show such a gun or any Model 1885 above Grade 5.
Perhaps you would get some Remington hammer gun expertise on the Remington Society of America web site --
https://www.remingtonsociety.org/forums/