Something I figured out some years ago as it concerns replica Cobras. You should NOT approach one to quickly with a tape measure. THINK about, do I really need to take this measurment? It will inevitably lead only to tears when you find one side higher than the other, one door different than the other and a myriad of other measurments (best left alone).
I was encouraged however when I discovered this same basic "measuring principle" can be applied to many of Detroit's cars as well! Just eye ball it, that's good enough for me (hide the tape).