On a valiant it is the v line above the wheelwheel, 1964 the line almost touches wheelwheel, 1965 the v line is higher up, and also closer the the top of the fender.
Darts im not absolutly positive but, 1964 had a headlight ring, "like 1963" and 1965 darts had what is called "candy kanes" 2 peice trim, and hood trim.
I have heard and seen few 1964 barracudas having 64 valiant style fenders, most 64 barracudas i have seen have 65 style fenders, im still not sure about this, i have seen early production cudas with a valiant emblem on the back. All 64-65 barracudas should have 65 style fenders, kinda interesting.