"Might it be possible it be a Coast Guard or Naval variant?"
As far as I know, no such creature.
No nickel plated Model 97s were ever made by the factory, and as far as I know, none were ever produced specifically for naval or Coast Guard service.
Also, it's not uncommon for Model 1897 riot guns, which WERE made in 1908, to be altered and passed off as "trench" guns. Some are very obviously marriages of parts, while others are quite elaborate fakes.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.