Nor do I believe any of the four (or more - but that's another story) of the First Indiana's "small steel-rifled guns" have survived. With great luck perhaps a photo image will show up. "Type 10" Blakelys would not have been "drop ins" for the Prairie carriage, however. Widths between rim-bases of the three surviving "Type 10s" are too great (8-8.9 inches) to fit a U.S. Prairie Carriage without adding 1 to almost 2 inches width between the cheeks, likely requiring some iron fabrication. Alternately, perhaps the small English carriages, which resembled the U.S. Prairie Carriage, were kept. I suspect the First Indiana's guns were slightly slimmer and longer (~39-40 inches) than the "Type 10" guns.
Notes from Pine Bluff Post Returns (30 Nov. 1863):
1st Indiana has 3 (three) 2-9/10 inch guns
5th Kansas has 6 (six) 4-62/100 inch
25[?]th Ohio Lt. Art. has 2 (two) 3-67/100 inch
That's 11 guns.
There's some 1864 Pine Bluff inventories (not detailed) in the O.R.s that hover around 11 (as I recall), going down by ONE (only) after Marks Mill.
30 January 1865:
2nd U.S. Arty (Col.) Co. H has 6 (six) field guns [no caliber]
(then there are some confounding January "Tri-monthly returns")
Tri-monthly returns for 10, 20, and 28 February, 1865, all agree the 2nd U.S. Artillery (H) has six field guns of a mix of 3.67-inch and 4.62-inch size. There is little change in this inventory until 31 May, 1865, Post Return, which adds 4 (four) heavy guns to the six field guns (total of 10) all with 2nd U.S. Artillery (H). May 20 & May 31 "Tri-monthly returns" reiterate the ten guns and specifies the calibers as 4.62" and 3.67". More-or-less the same until 10 September, 1865, & there-after when there is no more artillery listed. (but I didn't go through the post-war returns). On some of the forms there is the option of specifying "Heavy", "Field", or "Mountain" guns, and none of the 1865 guns ever is listed in the "Mountain" column. The 4 "Heavy" guns would seem to have been of no greater than 4.62" bore.
The only other weaponry-related note I found was (for example) in 20 August 1865, the 79th U.S. Col. Infty was armed with 460 .69-inch cal. muskets ( rifled or smooth bore not stated).
I've sent the film back to U. Arkansas library where it's available to all!