Boer War help please

[bearkin]

I am trying to find out more about my Great Grandfather William (Henry?) Clark (b1866). We know he served in the Boer War, but know nothing more. According to Chelsea Hospital, he served at in the King's Own Yorkshire Light Infantry and Rifle Brigade.  We do not know in which of these he served in during the Boer War. We know he was a reservist just before the Boer War and was probably called back into active service. I would be most grateful for any help/pointers in finding out more about his war service and about the roles, if any, of these units in the Boer War.

Thanks,

Pete