While I don't see a William Wallen, there is a W. Wall in the cemetery records and a William Walls on the list of applicants to the Confederate Home, so perhaps the name was misspelled in the records. If your ancestor was born in 1840, served in the 3rd Missouri Infantry, Co. F, was admitted to the Confederate Home in 1912 and died in 1913, then you may have a match.
Cemetery records - Confederate Memorial Cemetery, Higginsville, MO:
http://web.archive.org/web/20060617230036/http://www.yourlaunchpad.com/terry/lafayette/confcem.htm
Applicants to the Confederate Soldiers Home, Higginsville, MO:
http://www.rootsweb.com/~mocivwar/1745confedhomehigginsville.htm
Confederate Memorial Cemetery, Higginsville, MO photos: