Possible Clues:

• Robbery target in Westerns
• Post carried by this Irishman up on coach
• One providing a sort of express delivery service?
• Sounds as if he's on rail
• Sounds as if he is on line for the post
• He's the one in line to get the post, by the sound of it
• That's the 11 down for him, by the sound of it
• Puffing Billy may not have been one, but he sounded like it
• Sounds as if he's unlikely to go off the rails