I bought a Vintage Air unit and had God's own nightmare installing it on my '73 FJ40. VA's prediction of "about a day" to install was a joke. Nothing fit correctly, and I had to send back the first compressor bracket, which was warped and did not line up. I consider myself a competent amateur mechanic, but I wondered if the problem was me until I talked to a friend of mine who is a master Toyota mechanic and does nothing but Land Cruisers. He has installed a half-dozen VA units and says that a couple, in late model FJ40s (i.e. '81-'83), just dropped right in, and others on earlier models were just as problematic as mine. He does stress that, once in, they all worked great.
The only question I was asked when I purchased the unit was if I had a two-groove harmonic balancer (crank pulley), which I did. I found out after the unit came that the second groove on my pulley--originally intended for an air pump--was too narrow for the ac belt. I had to buy and install the proper balancer. Not cheap, even used.
I also found out after I got the unit that I lost both my sources of fresh air with this installation--the original fresh air intake setting on the fan and the cowl vent as well (the brochure said that "early-1968-models lose the cowl intake.") I am currently working on a fabricated lever to restore my cowl intake. The ad also said the unit has separate heater outlets. Not mine.
If I were to do this again I would investigate the more expensive aftermarket unit that duplicates the factory setup.