Try the receiver once separated.
Marocchi
It will be marked on the botton of the receiver.
What do you want to know? You can ask Marocchi at info@marocchiarms.com or contact the importer,Precision Sales International of Westfield, MA.
Browning.com has a sn function under customer service. It will be marked where it was made.
The Stevens Model 520 was built on a Browning patent and so marked. Stevens also built the gun for Sears before World War II under the 'Ranger' tradename, so if you have a slide-action shotgun marked 'Ranger' and 'Browning Patent' then that is what you have.
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.
No published sn data that I am aware of.
500
Most guns in good shape are selling for $350.00 up
Under $100. sales@countrygunsmith.net
Iver Johnson can not be dated simply by serial number. There is considerable overlap and even repeating over the years. Would need to know exactly how is marked, including the additional markings under the grips.
You need to get it lettered by Browning.