Even if you don't have any luck finding out his regiment, you don't need to know that to look for his service record. The Soldiers' Documents in series WO97 at The National Archives are arranged alphabetically and not by regiment from 1882 to 1900, then another series 1901-1913. So if he survived the army, you should be able to find him on the basis of the information you already have. The only catch is that you have to go to Kew to do it, or get someone to go on your behalf, because they are original documents and haven't been filmed or scanned.
If you have access to a library or record office that has a copy of the Army List for 1891, you can use this to find out what regiments were in the barracks at the time of the census. The easiest way is to find the names of the officers at the beginning of the enumeration book for ther barracks and look them up in the index.
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