So are the mirror cables (long for 2-door w/mirror placed ahead of leading edge of vent wing; short for 4-door w/mirror placed behind trailing edge of vent wing).
Properly, the mirror you're after is one-year-only. The shape of the housing changed a bit for '65, and then again a bit for '66, and then stayed the same til the last A-body in '76. But the differences are minor; from six feet away they all look alike, so your interchange on that mirror is '64-'76 A-body.