I've seen a conversion or two similar to this before.
Definitly NOT factory. Probably done by a gunsmith many years ago.
Looks to be a pretty decent job.
Would be a real fun revolver to own, but given that Army Specials don't bring big bucks, and it's been modified, I wouldn't expect it to fetch a whole lot.
I might give $300-ish myself due to the novelty of it ... and it's kind of cool. That's provided it's mechanicly sound.
Maybe someone else would pay more, but that would be top dollar for me.