that`s because the fastbacks were made famous by the 426 hemi cars, they didn`t ever come in a coupe ! That's why they are more popular. Even rarer was the two 68 383 form S fastbacks that came out with the 335 horse roadrunner engine , that was downgraded to 330 because of the drivers side exhaust manifold. The window sticker said exactly that , if I`d known what I had , I WOULD HAVE KEPT IT , ONLY HEARD OF ONE OTHER !! Was almost uncontrollable on that days tires, had to drive it or get out of it .