The grilles are very similar (mount to the same headlight buckets). The hood latches (but not the hood latch brace) is different. If you have a 65 grille and 65 hood latch, it is a straight bolt over change. Likewise with a 66. Now the 65 horse and corral will not fit to a 66 grille and v/s/vs.
The latch is the same but the top plate the latch bolts to is specific for '65 and '66. The '65 is taller and another thin bracket is bolted on top so the top of the '65 grill ornament can be bolted to it.
The '66 latch bracket is shorter in height and the grill bolts direct to it.