For my money it's not just the rooflines (on *all* the GM "C's, and "B" coupes!) but that amazing A-pillar! And contrary to what some Mean Girls, uh, dogs, say, the 1961 GMs are dazzling!
I remember drawing sketch after sketch of the Caddies of those years as early as FIRST GRaDE, seeing them passing my classroom window and dreaming. That would be 1962-63. Thanks for recharging my memories. 😊
1961 was just the worst of the 59-76 big caddy's! Horizontal tail lights and non-descript front grill makes this look like a GMC generic car. 1963 was so much better!