The new GT, as tested by Road and track, is now the second fastest road going current production car in the world, behind the Ferrari Enzo. Considering that you could buy three GT's for what you'll spend for an Enzo, I think it's a pretty good bargain.
I looked into building a Cobra replica a few years ago, with a 351 stroked and bored out to 427. ERA and Superformance had the best kits I think, although not the cheapest. Factory Five racing makes a nice kit that uses lots of bits from late 80's/early 90's Mustangs, but the proportions of the car just don't look quit right to me. What finally turned me off to it was that every car show I went to, I was seeing more and more Cobra's. Now, they're everywhere, at least around my area, there's no exclusivity left in them, unless you're filthy rich and own a real one. Prices I've seen lately for a driver quality 289 car are between 150K and 200K, 427's easily pull over half a mill, especially if they have history. Jeez, 426 hemi Cuda convertibles are going for over a million, 20 years ago who would have thought that would happen.