they made a coupe in 65 but it was called a valiant then, i beleive the 100 series had the same body lines and wheel base as the barracuda. though i'm not 100% on this.
as for the rear window have you tried looking for a used one?
You are talking about the fastback glass? ...not the back seat window.... right?
If so, I talked to a guy in southern Indiana about a year ago, and he had a rear '65 Cuda glass........ he asked me if I (or anyone that I knew of ) needed it. If you can't find one, let me know.
I'll have to scrounge around to find a way to contact the guy, but I didn't get the feeling that he wanted an arm and a leg for it.