I doubt the gun has a serial number the one I had just like it didn't. It was probably made between 1850 and 1860.
In the second set of picks it's easy to see why you had your hopes up....if it's any consolation I've had my hopes destroyed more than once in a gun purchase.
As far as Rockdoc being an expert on muzzle loaders....well I'm betting you're looking at his 'one horse ride'.
And as far as his "proof testing" it doesn't prove anything other than it didn't blow up that time....if anything it just puts undue stress on a 150+ year old gun.
No doubt you could probably get the gun shooting but ask yourself then what do you have ?
Ps...They are so enamored maybe InferO' Ed or Rockdoc will buy it and bail you out ?