Is this the car:
http://www.buyavette.net/1967%20Shel...067-115956.php
If so, let me assure you: This car is NOT A SHELBY! Those plates can be acquired on the street and attached to anything. The number on that plate is not a CSX number. Where did you see a CSXnnnn stamping? Understand that it is a Cobra replica but not a Shelby car of any kind. The dash is a dead giveaway. This isn't a barn find waiting to fund your retirement account
Is it a Shell Valley? Probably, but there are lots of Cobra replica builders out there so find an inspector that is well versed in the lesser known replicas.