There is some confusion here.
Chris, when you were advised that it "has to be either Navy or Artillery", the statement was in regards to what a pistol would "have to be" in order to qualify for the BATFE exemption concerning the mounting of a butt stock to it. This has nothing to do with its configuration/what variation your pistol is. Everyone's advice so far has been correct, although some could have been more clearly expressed; so there is no conflict.
Its worth is around a thousand dollars, I'd say, and I hope I haven't missed some detail about it. If you need to insure it, go to
http://www.simpsonltd.com/index.php?cPath=179 and find an "Alphabet Commercial" in similar condition for price/comparison. Simpson Ltd prices generally run higher than in the collector arena, but some find the extra money worth it in terms of dealing with a very reputable seller which stands behind their wares.