It's from a '73 manual. It looks like they changed the measurement procedure in '75, maybe had something to do with the cars that had the rubber isolated K frame? Or maybe the bent T-bar F cars?
Regardless, the factory ride height IS really high. My ride height is set so my A-B is 0, and it's still not slammed on the ground.
As far as the ride height and alignment goes, I've done it both ways. If you're driving the car 90% of the time with a certain weight distribution, it makes sense to set ride height and the alignment with that weight configuration.