Shotguns made in the US before 1968 were not required to have serial numbers. Would have to go with whatever markings are on the gun.
If data has been published, you might be able to find out the date made and specific model.
Impossible to answer without knowing who made it.
Not with the just the information you have given. Provide a detailed description of ALL markings, stock, barrel length, gauge, finish, accessories, etc.
Try the receiver, barrel, forend