I suggest you try your library for a copy of Art W. Bergeron, Jr.'s book - "Guide to Louisiana Confederate Military Units 1861-1865 (LSU Press 1989). Captain Kelso is mentioned in two places: 1) Capt. Co. B of the 2nd LA Infantry - until released after the reorganization of April 30, 1862. 2) He joined the 12th Battalion (Confederate Guards Response Battalion) as Capt. of Co. E in June or July of 1863. There is no mention of Capt. Kelso being associated with a heavy artillery unit that I could find. A Capt. King also joined the 12th Battalion in June/July of 1863 (Co. D - St. Martin's Parish) as the commander of a heavy artillery company.

The Bergeron book contains this information. I am confident that there are other Msg board participants that know much more about this and will provide your their input.

Best regards