What Mercedes manual do you have? The W126 CD manual has everything you need for the 603.961 and 603.971.

Replacing the head is not rocket science so don't be intimidated.

The 603.971 head requires different prechambers which require different injectors, or reshaping the 603.961 prechambers.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD