The Mercedes Factory "Time Guide" lists king pin and bushing replacement at 0.9 hrs. per side. Realize these times were for new cars, by factory trained mechanics, under perfect working conditions and with all the special tools and equipment on hand. For the rest of the world, just triple this time to 2.7 hrs. per side. Now if it is your first time you may need to double it to 5.4 hrs. per side. Since these cars are fifty years old, you will find other worn and rusted parts, like upper and lower link pins and bushings. Include repacking and or replacing of the front wheel bearings. Maybe do the front brake hoses while your in there. Yes, 10 to 20 hrs. is a possibility. Without any surprises or additional work, figure 4 to 8 hours by an experienced and well equipped technician.