Now that I think about it, the '58 and '59 don't look anything alike. The '63 and '64 don't really either. D'oh!

I stand by the other groupings though:
1955-56 - Basically the same except for the grille and turn signal housings
1961-62 - Same fenders, hood, roofline, doors.
1965-67 - Lots of differences, but the average Joe will mostly notice the similar headlights and sharper body lines that these models share.