If it were my car, I'd set the piston before head removal.
There are all kinds of theories about getting the spark plug resistor tips off 103's. One person who was a regular here a few yrs. back claimed he pulled them off with his hands. I must be weak.
Anyway, the MB part # for their contraption is 103 589 00 37 00, but I personally believe that Hazet # 1849 - 195mm gets them off quicker and easier. Before you reinstall coat the outer ceramic portion of the plug with dilectric grease as well as the inner part of the resistor tip or follow the directions on the tube of dilectric grease.
http://www.baumtools.com
is but one provider of MB tools to include the 2 I've mentioned.