ALL 1977-1979 2 door Chevy Impalas and Caprices came with the curved / bent wrap around rear window. 

Follow these instructions to see pictures, production numbers and VIN information for the 77-79 Caprices

Go to google, type in geocities 1978 caprice, go to Gallery of Caprice Classic's (it should be the first one)

Follow these instructions to see dealer brochures of the 77-79 Caprices and Impalas.  These show that this particular window was standard on all 2 doors

Go to google, type in fedrelandsvennen 1978 caprice, go to 1978 Chevrolet Caprice Classis / Impala (it should be the first one.  For 1977, change the 78 to 77 (this only shows 1 picture, but it does show the back window clearly).  For 1979, change the 78 (or 77) to 79 and where it says cap (after the 77 or 78), make sure to put an r at the end so that it reads 79capr.