The Favorite series is composed of many different variations, some only differing in the sights. The #21 Ladies Model is actually quite rare, but is often confused with the #21 Bicycle Rifle. They are marked similarly, but the Ladies Model has a vernier tang sight, high grade walnut stock and a Swiss buttplate. Digital pictures would help. firstname.lastname@example.org
It should be in the right side of the receiver, (small numbers)
All my records indicate that stevens did not make a model 337 shotgun.If your stevens shotgun is marked U337 under the receiver,this would be a serial number,not a model number.
Stevens 12 ga, Model 77D, made before 1968 may not have a serial number. However, some do! If it has a serial number, it will be behind the trigger on the receiver side.
Check the receiver and barrel.
The model number is stamped on the right side of the receiver on many Stevens products.
Check the barrel and receiver. Sn's were not required before 1968
You can try WWW.savageparts.comthey handle a large number of parts for savage Stevens arms
I do not believe the model 325's were manufactured after 1968. Therefore they required no serial number and yours may not have one. If it did have a serial number it would be on the receiver.
Serial numbers were not required at that time.
Look on the top of the receiver with the gun disassembled. You should find it there.
From the information I can find, if it was made before 1968, it probably doesn't have a serial number. In most cases, the serial number on a gun is pretty well out in the open and visable, usually on the receiver.