First, welcome to the S&W Forum. From your posting, you seem to be more sure of the gun's provenance than anyone who has seen it here, and I have to admit I've never seen anything like it. Perhaps you can provide us with a bit more of the gun's history and documentation? If you need definitive documentation beyond what you currently have, a factory letter is the gold standard of identification.
As far as pricing. That would definitely be what the market would bring. All you need is an auction and two enthusiastic bidders with deep pockets and you can find its value
Regards,
Green Frog