Is it because of different chamber sizes or are they physically not interchangeable and won’t fit ?
Most Ithaca 37's won't interchange with other Ithaca 37's.
I believe the only interchangeable 37 barrels do not have a serial number on the barrel and the actions have the serial number... the number somewhere after 855,000...
previous to that the barrels were individually fitted to the action and did not swap with others...