Hi Mark
I checked the Boer War medal roll for the cavalry after seeing the photograph. There are a number of Overtons listed. There are two As – Corporal 3337 in the 19th Hussars (he was in the siege of Ladysmith, so was there at the start), and 4709 Private in the 17th Lancers – he was only there in 1902.
There is also a 1991 Trooper FC Overton in the 1st Life Guards. Findmypast are due to publish records for men discharged 1900 to 1913 this month. You should find one or two in these. They have already published those for men discharged 1883 to 1900, and other periods will follow.
The lower the number the older they are.
Ken