Questions on Adding A/C

[thefarmboy21]

I've got an 86 K20 that I'd like to add air conditioning to. I've got two parts cabs (87 R10 & 83 C10) , both with AC from factory. Other than the actual heater box and the vents, what all needs swapped? Where do I tap the wiring into? What all is recommended I replace off the bat? I'm really not sure if either cab has all the wiring. But both seem to have most of the parts on the firewall.

[zieg85]

The firewall holes are totally different for the AC versus non-AC cabs