Your best bet is to apply to the National Archives (or hire a military researcher to do so) to dig out this man's attestation and service papers from series WO 128 which is the Imperial Yeomanry series. Unlike those of regular soldiers, papers of IY men who died on service have survived. This series isn't available online but these papers will confirm place of birth, age on enlistment and other details, usually including name and address of next of kin, that would enable you to confirm whether or not he's your man.
David