It is a Model 1894 action, but I think the barrel is later - the last catalog I have with the 1894 still has the company name as 'J. Stevens A & T CO."' and not 'J. Stevens Arms Company' as stamped on your barrel. Also they did not list full round barrels as available, just the part octagon ones (not true octagon, the bottom of the 'octagon' part is round). The barrel lengths offered were 24" standard and 26" optional. I see the front dovetail has machining marks showing it was done in two passes, but looking at a couple early Stevens barrels it appears they did do the wider front dovetails in two passes. It might be an added dovetail that got cut wrong, or the original got widened for some special sight. You are correct that it should be 7/16" on a Favorite. I can't think of any sights that used that wide a dovetail, it's almost 9/16".
ADDED - that barrel is possibly from a Model 1915 Favorite. The 1915's had a breech bolt that was straight on top. Round and full (true) octagon 24" barrels were offered on the Model 1915 (from a 1927 catalog).
Last edited by GeneB; 03/28/24.