As Lighter says, there is no evidence that "Sulloon" (and var.) would indicate pre-Civil War age. As I stated, the Royal Irish were there until 1866; other units with Irish soldiers certainly were in the Raj and Ceylon until those regions became independent in the 20th c. Moreover, units with a base there were sent into other theatres of operation, and then returned.
There is little room for speculation, since no specific actions are mentioned in the song.