You are correct! I would have never thought that there were so many John King and J. King listings, in Al. Units.
His widow's application for his pension listed him with the 6th Al CAvalry. I have a J. G. King; pvt. Co. C; 6th Al. Cavalry. His compiled service records may, I repeat may, give you a clue. These records can be found on microfilm in most major libraries in Al. His National Archives Box, Roll and Number are as follows: 000374, 0024, 00003558. These numbers may be of help if you live near a regional office of the National Archives, Atlanta, Dalla/Fort Worth, Kansas City etc.

Good luck

Wayne Adams