Thomas,
Great find! The gun looks to be in great condition.
I had the chance to inspect and make an offer on a similar gun about a year ago in Syracuse. It was a serial number right around 1,000 if I remember correctly. It was an open ended offer and I never heard back from the seller. It would not be too hard to get all the accessories to complete what is missing. The most expensive part would be getting all the missing shells.
But the value may be diminished since the shells would not be original to the set.