Complex sentence: The 1920 census backs up his claim, and a possible 1910 census match, if the right person, also does.If his claim is true, he would be the last survivor of a Alabama regiment by 34 days.
Split into simpler sentences: The 1920 census backs up his claim, and there is a possible 1910 census match. If there is indeed evidence that he actually served in the confederate armed forces, he would be the last survivor from Alabama and the confederacy by 34 days.