Yep, I always look for the "egg crate" grill to distinguish the '66 from the '67, but the headlights are a good tell also.
If Ian's dad's car had a 455, it was a '68 or later. The '66 and '67 had the 425 (Which was a great engine BTW).
The same friend who had the GS also had a '66 and a '70 Toronado.
