I am replacing the gearbox I need to know what the replacement fluid capacity is for the power steering?

It's funny -- the workshop manual does not share capacity of the steering system. But it also indicates 4 different power steering gears possible to be equipped in the vehicle, so -- my advice would be to obtain about 2 or 3 quarts of power steering fluid for General Motors vehicles of this vintage an fill the system - purging air and topping off to the full mark.