About the Lady Baxter: it was a "strange" piece.
Olmstead, Stark & Tucker, The Big Guns [source for nearly eveything below], p. 67, has a sub-chapter about it (her?):
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8-inch naval Columbiad
A singular unmarked 8-inch smoothbore at the Old State House in Little Rock, Arkansas, is locally identified as the "Lady Baxter". Some of its dimensions approximate those of the corresponding United States Pattern 1857 New Columbiad. Original trunnions, presumably broken off to disable the piece, are replaced by a rough forged wrought-iron trunnion band. Much of its muzzle swell is crudely chipped away as if to give added clearance through an embrasure. Its rounded cascabel includes breeching jaws, block, and pin for naval service.
Leeds & Co., employing 300, was the largest manufacturing firm in New Orleans. It reportedly made "a few heavy guns for the Navy". One such 8-inch Columbiad burst on its 76th charge in proof, making it about as durable as corresponding Federal Columbiads. Bennett & Lurges ["Surges" in OR] also cast five 8-inch. When New Orleans fell, on 29 April 1862, Bujac & Bennett was reportedly preparing to produce an 11-inch.
[Original source includes "OR 1:VI:576, 584, 621" i.e. excerpts from the witch-hunting Court of Inquiry about the fall of New Orleans - that BTW was presided by Hindman. There are many other references to New Orleans-produced artillery scattered here and there in this long OR chapter, as well in the corresponding NOR one. But details are very sketchy, and many witnesses looks naive, misinformed and vague, when not positively reticent]
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So we are said the Lady Baxter had "some of its dimensions" approximating those of the corresponding United States Pattern 1857 New Columbiad. Those of the 8-inch flavour were: ~120.5" length [#1], 25" diameter, 9,100 pounds weight.
However, looking at the photography in my source, at first glance this gun is not an [Army] Columbiad at all. Besides its evident naval cascabel, its shape looks much like a [Navy] Dahlgren shell gun. The Dahlgren of similar calibre [VIII-inch in Navy parlance] was 108" x 24.2" x 6,000 pds, quite smaller. A comparable piece is the IX-inch instead, 120.9" x 27" x 9,200 pds.
A better look at the photograph reveals that the piece resembles a Dahlgren, but is not a real one. The most obvious difference is the presence of an astragal, or chase band (the ring near the muzzle). A vestigial remains of XV century, at last eliminated in Dahlgren designs but perversely kept by our unidentified New Orleans foundry. This reveals they were not aware of latest developments in artillery and/or had little experience. Definitely they had not access to the original drawings.
[#1] The exact length of a gun seems to be a matter of opinion. The (approximate) number I present here, inferred from drawings in my source, is the maximum total one, less the length of the rear appendix ["cascabel"]. Why? Because naval-type cascabel is much longer than army-type one, hindering comparison.
Let's assume our Lady Baxter is just one of a few similar or identical pieces sent to Arkansas. According to CSN Investigations:
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[nori1_468] Captain Mitchell: [...] I would say in connection with the answer to the question respecting ordnance that one gun was cast there and offered to the Navy. It burst, however, on the first trial. It was cast by Leeds. There were some other guns cast there before I had anything to do with the station and put on board of our vessels, and I believe that some of them also burst. There were some six or eight of them altogether; some were put on board the Maurepas, the Pontchartrain, and the Livingston.
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If C.S.S. Maurepas embarked one (or maybe two) of them, it would confirm the following statements:
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[nor23_188] U. S. GUNBOAT LEXINGTON, Clarendon, Ark., July 2, 1862.
Flag-Officer C. H. DAVIS, Commanding U. S. Naval Forces on Western Waters, Memphis.
[...]. At St. Charles I propose to take on board this vessel a new pattern VIII-inch gun, now on the bow of the wreck of the Maurepas. [...]
I have the honor to be, sir, your obedient servant, JAMES W. STORK, Lieutenant, Commanding [U.S.S. Lexington].
["New Pattern" meaning, to a 1862 Navy man, a Dahlgren, opposite to the old 1845 pattern]
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[nor23_192] U. S. GUNBOAT LEXINGTON, St. Charles, Ark., July 9, 1862.
Flag-Officer CHARLES H. DAVIS, Commanding U. S. Naval Forces on Western Waters.
[...] We arrived at this place at 4 p.m. I will now take on board, if possible, the two guns on the bow of the Maurepas. [...]
JAMES W. SHIRK, Lieutenant, Commanding [U.S.S. Lexington].
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Also, if these were the heavy guns captured at Fort Hindman, it would explain why they were identified as either 9-inch or 8-inch in different Federal reports: the former if you compare its exterior size with a similar piece you are familiar with; the latter if you take the trouble of measuring its bore.
Just a suggestion.
According to my counting, total number of such (or similar) heavy, anti-ship, guns present in Arkansas would have been:
White River:
- 2x 32-pdr/42-pdr rifle, disembarked from C.S.S. Pontchartrain, at Saint Charles since ?, captured 17 July 1862. [see message #2]
- 1x or 2x 8-inch, left onboard C.S.S. Maurepas, scuttled at Saint Charles 17 July 1862.
- 2x 8-inch (from ?) at Devall's Bluff, since at least 19 June 1862 [ar19_836] to January 1863, evacuated to Des Arc and captured there 16 January 1863 [nor24_157].
Arkansas River:
- 3x 8-inch/9-inch (at least 2 disembarked from C.S.S. Pontchartrain) at Fort Hindman (Arkansas Post), since fall 1862, captured 11 January 1863.
- 2x 8-inch/9-inch (salvaged from Fort Hindman, so already accounted for) at Fort Pleasant (Pine Bluff), since early 1863, evacuated to Little Rock July 1863.