No big deal. Where are you located and I'll come help for the price of the A/C if it's factory!! If you want I'll even find the parts to fill in the "holes" left from the A/C (but only for first dibs on the A/C).
Depends on how mechanically inclined you are, especially if it works and you want to sell a complete, working unit. If your favorite tool is the blue-tipped wrench and you are trashing it, I'd say pretty easy and could be done pretty quick.
It just takes common hand tools. Back in the day I bought a Toyota kit for my 87 4X4 pickup and it was pretty easy to install.
There was no oem a/c in the United States prior to the 79 model year. Take a pic of your unit and post it, I have one for sale that's aftermarket, but only the in car portion, you'd need your own compressor etc.