Taillights, front fenders and grille are different. You can put a 64 grille on a 65, though - and I think the 64 grille looks better. You could also swap fenders, just know that the hairpin on the 64 Valiant is larger than the 65 Valiant (which is the same as 64-65 Barracuda). Dashboard gauge cluster is also different, and a 64 with automatic trans will have pushbuttons while 65 will have a column or floor shift. Heater controls are different.
Mechanical is all swappable, as are most other body parts, including bumpers, doors, quarters, hood and trunk lid and (as far as I know) glass.
