The entire front clip is required -fenders, grille and brackets, hood, headlight buckets, core support, trim etc etc . It is fairly easy. For 64 to 65 and vice versa.
I had the option of making my 65 a 64 front end but decided not to. Had to buy a few pieces original used (headlight buckets and grill brackets) due to not being reproduced. Luckily i had 65 fenders and hood to start with. Most front clip items a repoped for 64-65.