Apparaently it is not based on the 65-66 fastback. I know the pics of the concept featured a red 65'66 fastback, which suggested that the inspiration for the 05 model came from there, but in any interviews i've read with the engineers, designers they all say its based on the more agressive 67-68 fastback.
In the february edition of Topgear magazine (UK) chief designer Larry Erickson says it harks back to the 67-68 models.
quote:
"Those are the cars everybody feels are the right ones, with the long bonnets and the short boot lids"
In my opinion the front half of it is very 67-68 but the rear half is like a cross between the 65-66 fastback and the 69-70 fastback.
Still like it and cant wait to see how it develops over the next few years. I believe in 10 years time there will be one model year of the new mustang that everyone thinks is the best one, dont think it'll be the first one though, maybe in 2 or 3 years they'll do something with it (like some of the GTR details) that just works perfectly, IMO!