They've got the full range of sizes in that model.
Principia make great frames but like andrewgturnbull says if it doesn't fit properly don't buy it. No amount of discount makes up for a poorly fitting frame.
Besides, you can get complete Lemonds for less than £600 and I'd expect them to go even cheaper now he's been dumped by Trek :-D
Looks lovely! Would be interested to know how the ride feels, compared to carbon framed effort.