I had a rewarding conversation with Trevor Jones this morning, and he pleasantly answered a few questions that I posed to him.
There is a steel vent insert (bouche) on the British bronze 3-pdr, but there's no documentation as to when, or why this was done. I suggested that it may have been installed sometime in the latter 1800's, or early 1900's, perhaps in preparation of firing the piece to celebrate, or honor some anniversary etc.
The only mark remaining on the tube is the English broad arrow, no other marks exist. He informed me that the gun is still polished (fairly obvious) as a regular maintenance procedure; and I told him that this was a controversial practice, which a vast majority of artillery collection curators do not presently follow.
The 'volley gun' is in excellent condition, except for the fact that one barrel is missing. This is entirely anecdotal according to Mr Jones, but the story is that sometime post Civil War, someone at the arsenal removed the barrel to use it as a fireplace poker, and it then got lost.
The 'Williams Gun' is definitely considered one of the museum's major artifacts, it was simply because of time constraints, that it wasn't shown on the C-Span video.
Open the link and type "williams" in the search box, (upper right corner) in order to view a couple photographs of the gun.
http://history.ky.gov/military/The museum is going to re-open on November 11, 2011 (Veterans Day) at 2:00 PM.