You don't need to replace the bolts unless they are over length. I don't have a factory manual to offer the exact length, but it should not be difficult to come up with here on the site.
If you pull the head ONLY, without the intake manifold attached, it was next to nothing, you will not need a helper to lower it in place. I think the previous poster was thinking of an iron head engine.
These engines have a ratcheting timing chain tensioner and give very few timing chain problems. They probably have the most reliable timing chain and associated components of ANY MB engine to date.
The previous poster is, of course, correct about looking for bent valves, but if there is one or more bent, I would suspect a broken valve spring as the cause, rather than a timing chain problem. It will be obvious when start taking it apart.
When you start back together with it, let us know and we will coach you on how to get the upper timing cover in place such that it does not leak.