It was the sample "new" car from AC when Jim Price (SPF) was trying to get that franchise into the US...
http://performanceunlimited.com/scof_news/newac.html
Kristen..
the designators are AC's way of ID-ing cars
The "C" denotes the product line
COX - original manufacture for Export
COB - original manufacture for sale in UK
The original Cobras carried CSX - with "S" for Shelby and "X" for eXport