The fuel injection system must be kept clean. Be careful when removing the pipes, takes lots of pics. You should have done this in the Vintage forum, but here goes.
Does anyone know if there is an online service manual that I can download?
It's available from Mercedes on CD. You will need the 1959 - 1968 CD and the later one as well. The later manuals are supplements to the PONTON one.
Are there other special tools other than the 10mm to take the head bolts out?
You need to remove all the valve components first. Screw down the valve adjusters and remove the finger followers and the small springs, bag and ID them. Do not mix and match.
Besides the headbolts, I have to set timing at TDC? , mark the cam sprocket where it aligns with the timing mark on the chain? ,
Replace the timing chain. Grind off one link and attach the new chain to the end. Rotate the engine and feed the new chin in. Watch those small circlips don't fall down the chain hosing, Stuff rags in there.
Is there a trick that you use to wedge the timing chain?
Do not wedge the timing chain. You would do well to replace the chain and guides. You will have to remove the tensioner as well. Check the sprockets for wear by looking at the tips. If they are sharp and pointed, replace them. If the ends are squared off, it's OK. Replacement guides are plastic. They are held in with pins. Check one of my other posts:
420SEL:
Chain Guides Replaced
220S:
220S M180 Engine Work
What else do I have to loosen besides the headbolts?
The throttle linkage needs to be removes. Do not make any adjustments to either the throttle stop or the injection pump stop. Use a small open ended wrench to pop the socket off the ball joint.
Should I leave the intake manifold attached to the head and remove later?
Remove the intake and exhaust manifold. Use new copper nuts. Watch those injection pipes. Consider sending the injectors out to be cleaned. They operate at approx 250psi.
Check this forum, same engine:
http://www.sl113.org/forums/