I found my setup from an 83 in the pick n pull. Make sure you get all the parts because some are hard to find otherwise.
evaporator box with evaporator coil, TXV, pressure switch and thermistor, electrical sub harness and amplifier board, mounting bracket, drain hose, wide band clamp to heater core housing, firewall grommets (consider replacing the TXV - easy to find)
2 rubber plugs for metal fresh air duct that runs across the front of the truck (3 or 4 inch diameter)
plastic ducting that runs under the dash including the clamp on the steering column and the center output duct with louvers (different for AC)
Heater fan control switch with AC control on it, knobs and faceplate
low pressure hose from comp to firewall
high pressure copper line from firewall to receiver/dryer with mounting clips
high pressure hose from comp to condenser (think about getting a new one made up if rubber is hard) this is the weak link.
condenser coil with rubber mounting hardware - (I got a new coil from Toyota because the used one I had was in bad shape)
L shaped tube from condenser to receiver/dryer
receiver/dryer (get a new one, easy to find)
receiver/dryer mounting bracket
compressor, there is a larger one for 4runner that requires a different bracket
compressor bracket with idler pulley - needs to match the compressor, get hardware that holds it to engine and the four compressor mount bolts. Bracket mounting bolts are longer than those currently installed.
belt
carb idle up actuator
VSV
The 79-81 version is different, it uses flared fittings vs o-ring (not sure if this applied in 81), the 20r carb idle up actuator is different from the 22r, and the AC dash control is slide vs rotary. The 79 steering column bracket to hold the duct is different also, and probably the vsv too, at least the connector.
I have a spare setup from a 79 I need to do something with, taking up garage space.
Let me know if you have any questions about the installation, it is very easy, like installing a kit. holes in the firewall are pre-dimpled so you know where to drill for the two lines and drain. Electrical is plug and play.