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I could be in error, but I believe your single-barrel shotgun to have originated as an N.R.Davis shotgun.
N.R. Davis & Sons was a small gun company started in the late 1800's, which moved (1914 ?) from Assonnet, MA to Norwich, CT, and later (1917 ?) became the Davis-Warner Co, then yet later (1922) was absorbed by Crescent Arms as the Crescent-Davis Co, then still later (1931) by Stevens Arms Co.
Yankee gunmakers have long been loathe to waste a red cent, so I would WAG that your unfinished action was in the Crescent Arms warehouse purchased by Stevens.
It's well-known that Stevens completed & finshed every gun they laid their hands on, whether as an "N.R.Davis & Sons" (one of which SxS' I once had), a "Crescent Arms Co" - or (in your case) a "Stevens Arms & Tool Co" gun of non-descriminate parts.
I seem to remember Stevens calling them the Model 140.
Here's another Stevens, in quite better condition, with the same action as yours:
http://www.gunbroker.com/Auction/Vie...Item=390796617
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