Walt Disney's Comics and Stories #6 (234)

Donald and his nephews volunteer to assist with the replaying of the pony express with Donald delivering the mail. The mail is planned to be fake, but Donald encounters a crashed plane and agrees to urgently deliver real government mail containing secret documents for the pilot. Unfortunately, the others involved in the pony express replay are not aware of Donald carrying real mail and proceed to ambush Donald at the pass as part of the re-enactment.