It may be the author is referring, by "pulleys---in---the---sky" to a logical impossibility.
A pulley is attached to some solid structure and by means of its wheels, is able to reduce the force needed to lift something heavy.
But of course, there is nothing in the sky to anchor or pin the pulley to. So the author is comparing some idea or proposition to something as absurd as Pulleys---In---The---Sky.
It is commonly a practical joke among working men and women to play a practical joke on a new employee. They will tell him or her something like this.
"Go down to the warehouse and tell them that we need a "Sky Pulley" and 100 feet
(about 30 meters) of Flight-Line to go with it. Also, do not come back without the
"Mumble Shears" for cutting the Sky Felt."
Of course, when the person asks for these things, which do not even exist, everybody laughs at the new person and tells them they are either crazy or an idiot.
The person returns to his fellow workers and says; "Ha, ha, ha! You guys are sooooo funny!"
Everybody has a good laugh. It may be for months that the others remind the new person about his embarrassing request. It is all in good fun though. Working people like to see if the new person can laugh at a joke. If the person does not laugh with them, they know the person will probably not get along well with others.