Those old Remingtons are not being made anymore. They are nice, solid steel works of art compared to some of todays offerings. If I wanted/needed a short barrel home defense gun the 870 Express or Mossberg 500 can be found fairly cheap and parts are everywhere.
If the old Remington is not now working reliably, how will it work after modification? The age of the Remington may suggest more repairs and parts needed in the future. Just my 2 cents worth.