This is a great part to get your hands on, as this is the most specialized bit in the whole aftermarket assy. Just keep in mind it's only about a quarter of whatcha need.
You still would need:
The compressor is a reciprocating unit by York. The condenser can be fabbed; the only hard part to source would be the A/C bracket; if need be I can make one up for a few bucks using Maggie's as a pattern.
The downer is the orig NOS system used R-12 as a refrigerant; the system would now require HCFC-134a which *can* work but the compressor has to be upgraded AND the condenser has to be enlarged to overcome the lower efficency of the 134a as a refrigerant.
The other downer is GT's have so-so cooling systems to start with; adding A/C imposes additional loads on the motor AND increases ambient temps to the radiator. The likelihood of overheating is significant, unless a supplemental cooling fan is added along with a 3-core radiator.
Expect the whole schmeer to cost $1200-$1500 when complete.