Oh, yeah. There is no way you can add A/C to the existing heat/vent system. There's nowhere near enough room in the heater boxes (underhood, behind dash) for an evaporator, and there's nowhere near enough room behind the dash for a box large enough to contain an evaporator. You'd have to tear out the entire dashboard and build new from scratch. It's been done—there was an extensively hot-rodded '61 Valiant a couple years ago—but the dash/interior work alone cost five big digits.
First year for integral Heat-defog-AC on the A-bodies was '65, and even then the system was undersized and kind of a tight squeeze because those cars weren't originally designed with integral A/C in mind...and they were much less crowded under the dash than the '60-'62 models.
