The big trucks came with a shroud and it is detailed in the 1954 Assembly Manual. Here are some pictures of the factory AD shrould. I have owned 3 of these never seen the one you show from eBay.

http://good-times.webshots.com/photo/2673348600102454676qtmVHy
http://good-times.webshots.com/photo/2725195130102454676geWBTw
http://good-times.webshots.com/photo/2705488650102454676sLCmCA