The Caprice used that roof line. I thought for sure it was a Caprice, sans badges, until I saw the Impala logo on the fender. The Impala is just one of four trim levels for the Chevrolet B-body. It starts with the Biscayne at the bottom, Bel Air is next, then the Impala and finally at the top of the food chain the Caprice. The Caprice was the Cadillac wanna be of the Chevy division; having the most trim and optional features on other Chevy's as standard equipment.
I have never figured out if it would be cheaper to order an Impala decked out with all of the Caprice standards, or to buy the Caprice model with it's different roof line. But some things such as the Fleur de Lis in the fabric and up until now I thought the Caprice roof were reserved to that trim line only.