Western Field was the house brand for Montgomery Wards. This shotgun was subcontracted to various manufacturers. Main one was Mossberg. I have one and it's a Mossberg 500. Recommend you contact either Numrich or Brownell's, both of whom have web sites. Both are major suppliers of gun parts and gunsmithing tools.
That number doesn't show up in the cross reference list however it's likely a Mossberg 500.
The value of a Western Field Model M55OAR 12 gauge shotgun typically ranges from $150 to $400, depending on its condition, age, and specific features. Factors such as whether it includes original packaging or accessories can also influence its worth. To get a more accurate estimate, it's advisable to check recent sales, consult firearms appraisal services, or visit local gun shops.