Once again, McAllister's Battery was Battery "D," 1st Illinois Light Artillery, not Battery "B."
I wrote the high school paper in November 1963. Among Captain McAllister's papers was a cabinet card photograph showing the Battery D monument and two howitzers. The photograph was taken from the front of the monument and the muzzles of the two guns. On the right was a 24-pounder howitzer, and on the left was a 12-pounder howitzer. Battery D was never equipped with 12-pounder guns and this was an incorrect placement by the Park Service. But, I wouldn't imagine that they had too many 24-pounder guns. McAllister had written [it was his own handwriting, verified by his elderly daughter, and similar to the handwriting in the rest of his papers] the following note on the side of the photograph under the 24-pounder howitzer "This gun belonged to McAllister's Battery and was in action here on April 6, 1862." The family story was that McAllister acquired the cabinet card when he visited Shiloh for the dedication of the park [more probably the Illinois monuments]. When he visited the monument he recognised the tube number on the 24-pounder gun. That would not necessarily surprise me, because a lot of us old soldiers can tell you the serial number(s) of weapons we carried in the military.
My parents attended a convention in Memphis in December 1964, and I drove out to Shiloh to tour the battlefield. Of course I visited the Battery D monument. At that time, a 24-pounder howitzer was still located on the right side of the monument and a 12-pounder howitzer on the left. I have no recollection of making any notes of the tube markings on the 24-pounder. Somewhere I have some photographs from the trip. From your [recent?] photographs, the Park Service has clearly moved things around since 1964, and perhaps they can track the tube numbers of the guns they moved. But, given the placements of the guns, I can't see why they would have gone to the effort to move the 24-pounder on the right side of the monument since there is still a 24-pounder gun there.
Regards,
Don Dixon