68 Fastback Window ???

Hmmm. did they possible give you the wrong year molding (i.e. gave you 66 instead of the 68 molding)?

The clips are the same for front to back on a coupe. I don't know about a fastback

I feel your pain man... I did the moldings with aftermarket kit about 7 years ago when i completed my restoration and I know how frustrating this can be. The aftermarket kits fit like sh$t. They don't engage the clips right, the bends in the corners aren't accurate enough to fit properly and they are just a bear to get on without damaging them. In the end, I manaed to get them on pretty good, but damaged parts of the molding by denting them trying to get them to engage the clips. I am keeping my eyes peeled at swap meets for factory stainless pieces and will polish them and hopefully get a better fit. I don't recall my pieces being short like you describe however. Good luck man and just remember, walk away and get a beer if you get too frustrated