A/C Question...
As far as install rates, it would be about 15-20% at most.
It was a $325 option and also reguired 7.00x13 tires which were standard on a V8 but $12.85 on sixes.
Seeing how a 273 4bbl engine package with power brakes and HD suspension was only $155, it was really expensive to have A/C.
Somebody else will have to step in about install difficulty as I am not familiar with the early A-Body A/C set-ups.