As the owner of an 'X' code '68 GT/CS, it's a great car. However, just so you're aware, none of the major Mustang parts suppliers carry parts unique to this engine. It's been a little tough to find some things I need, like the exh. man. to carb tube. In fact, many Mustang books do not even acknowledge that this engine was available in the '68 Mustangs. As per Kevin Marti, 476 Mustangs (out of about 4,000 GT/CS's, and about 317,000 '68 Mustangs) were 'X' code. So it is super-rare. I'm also a realist: that does not make them super-valuable!