It looks like you have what was marketed as a Field Grade / Waterfowler gun - IOW, a somewhat specialized repeater for longer-range waterfowl hunting/shooting, like pass-shooting Duck and/or Goose (A popular hunting pastime after WWII).
It wouldn't have been a "special order" gun, by any means - just a different model than the rest of the Model 37 line at the time - although since a dealer might not normally carry that model, if a customer wanted one, it would have to be ordered through some wholesaler, etc.
There's no special collector's value attributed to it (over/above most other M37's in like condition), so use it as you wish, or alter it if you want, since the value wouldn't change very much no matter - just be aware that if the barrel's shortened, you'll lose any choking, ending up with a cylinder bore (best suitable for close shooting, deer slugs with sights, or HD).
Also FYI - Model 37's of that age are susceptible to jamming if "short-stroked", so pump it like you mean it (or it owes you money
AND, since they had no disconnector, if the trigger's held back and the slide handle's pumped vigorously, the gun will "slamfire" every time it's pumped - permitting very rapid fire, indeed.