Good points, and you are probably right, although I suspect that none of the armament was shipped over from other vessels, as I think that would have been mentioned. Of the three descriptions of armament I've got in front of me, I've got three DIFFERENT descriptions, none of which mention the 6-inch rifles as being Brooke rifles. Now that I think about it, I'm not sure where I got it in my head that they WERE Brookes.

C.W. Read:
“Reminiscences of the Confederate States Navy” - Southern Historical Society Papers - Vol 1

Forward
2 - 8-inch Columbiads

Broadside
2 - 9-inch Dahlgren shell guns
2 - 6-inch rifles
2 - 32-pounder smooth bore

Aft
2 - 6-inch rifles

George W. Gift
"The Story of the Arkansas" - Southern Historical Society Papers - Vol 12

2 - 8-inch Columbiads
1 - 8-inch shell gun
2 - 9-inch shell guns
1 - 32-pounder smooth bore
4 - Rifle Guns (described as "formerly 32-pounders, but now altered, three banded and one unbanded")

Captain Isaac N. Brown
“The Confederate Gun-Boat ‘Arkansas’” - Battles and Leaders of the Civil War - Vol 3

Forward
2 - 8-inch, 64-pounders

Broadside
4 - 100-pounder Columbiads
1 - 6-inch naval gun

Aft
2 - Rifled 32-pounders (described as "old smooth-bores banded and rifled")

Isn't research FUN??