Best lef to a gunsmith
Go to Google, select IMAGES from the toolbar, and for search term enter Iver Johnson double hammer shotgun.
Manufactured sometime between 1920 and 1948.
I have two 1878 Jas Parker & Sons double barrel shotguns.
they are selling at auction for around 300.00
You will need a professional appraisal
Seldom go beyond 150 USD
Your Iver Johnson double barrel shotgun can be dated by the words hammer forged.This places production from 1936-1941.these were well made mass produced field grade shotguns of high quality.
Not listed in any references I have.
50-100 USD or so