I'm not sure about the V8's but all the MB engines I've worked on have stretch bolts. They are really tough to get loose and maybe tougher to retorque, using the proper angle torque method. You will need to get a manual for your engine before going back together.
You will need the correct tool that fits the bolts properly. This is available as a MB tool, but a friend of mine found a set at an auto store that had about three different sizes and one of them fit perfectly. Much less expensive than the MB tool.
Use the correct socket, a long breakover bar and plenty of oomph. They'll come loose.