The head has to be removed to get the pistons and rods out.
I would strongly suggest to start with obtaining a good repair manual, like the Mercedes DVD.

Taking the head off is not that hard.
1- remove distributor cap and rotor
2- remove rotor bracket (small torx 5 or 6 mm, use a good socket)
3- remove top front cover
4- remove chain tensioner
5- remove rocker arm brackets
6- remove the bolds from the camshaft gear (chain wheel)
7- take the wheel out.
8- remove the top pin from the plastic chain guide
9- remove all bolds holding the head
10- lift the head.

Rob