Old thread, new information....Larry is correct that the early cars were twin stack - first photo posted by Rick Parker above. Here’s why - the early cars used the no hole 221-260 (and very early 289 in 1963) style valve covers when these engines had the
oil filler in the timing chain cover and used a road draft tube. These no hole covers were also on the 100 or less 260 XHP engines supplied to Shelby American. These no hole early covers are getting tough to find. The second type with the single stack are based on the more familiar 289 style Ford valve cover with the hole in the raised ‘mesa’.