If it were an easy project your mechanic would have fixed it and sold the car. The reason that it takes 21 hours is because the whole dash and console comes out, the 140 body is not a 123. The self leveling was an option, but the car should only slightly droop. The leveling pump is tandem to the power steering pump. Considering what it would cost you would be lucky to break even. I would spend the $150 and buy the 140 DVD, there are no paper manuals.
http://www.startekinfo.com/StarTek/