that is definately not a 58 chevy (i have 2 of them) a 58 chevy does not have the chrome running on top of the fenders or does not have the body line in the center of the hood. i agree its a caddy.
The Impala and Coupe de ville look qutie similar..but without seeing more of it I really cant tell....I'm really not seeing any fins on the back...and thats where they do differ.
That's a '58 Cadillac 2-door hardtop Coupe De-ville! you can tell by the cowl and the mold line on the quarter panel. you can also faintly see the fin covered up by whatever debris is piled upon it's deck lid! OMG Somebody save it!