The slide release is on the side of the receiver, instead of behind the trigger guard.
Looking for replacement Stevens shotgun parts? Numrich has a huge selection of Savage/Stevens/Springfield shotgun parts for sale and has been a leader in providing new and used parts to the shooting community since 1950. This one is a straight 520, and predates WWI. A group of Western Field sb033 12 ga parts these are the Stevens model 520 if you want any of these parts send me a email at thanks.