The real issue that you are dealing with here is that Ithacas were all built on their own size receiver. The 12s,16s and 20s had unique sized receivers, barrels, mag tubes, stocks, foreends, etc. There are some internal parts to the receiver that are interchangeable, such as the trigger pack (has to be either a 2 3/4 or 3 in trigger pack depending on chambering) and some of the springs. Even the guns chambered for 2 3/4 or 3 in had different length receivers (3 in added 1/4 in to the original design) and that changed some of the components and unless you know which are which and understand the differences, you can buy parts and they simply won't fit, or will fit and won't let the gun function.
That gun is an interchangeable barrel gun. Since the serial nbr starts with 371xxx, it is well after the 855,000 cutoff. You can buy a different barrel and simply turn it into a field gun. That gun is a 2 3/4 in chambered gun otherwise it would say MAG-371xxxx or 371xxxx-MAG. A 3" chambered barrel will fit it and function, but it will still only function with 2 3/4" shells.
It is not really a good platform to build a "tactical" shotgun on. You cannot get an extension for the mag tube due to the design, etc etc.
Its value is in trade, yes in trade as it is not a highly desirable Ithaca OR, and most importantly, it can be turned into a field gun if you hunt or shoot trap or clays.
If you are wanting to build a tactical gun, and can get a good trade out of it, go for it.
Or get a another barrel and and turn it into a field gun, just make sure you don't get a barrel with a 6 digit serial nbr on it, 855,000 or less.