I am not familiar with the B7100 but will try to help based on my limited experience with a different model.
Definitely need a Workshop Manual and illustrated parts list. Some of the numbers on parts will change and you will need to cross-reference up to those.
I believe that on your model the head gasket also has a shim. You may need a gasket for the muffler if you remove it. The intake manifold and exhaust manifold may or may not need to be removed. Also water cooling. Cover has a gasket.
You may get lucky and find the problem is only the gasket/shim. Plan on some work getting the block and head clean, really clean, for the new gasket. Do not use wire brush, brillo pads, starbrite pads, anything hard or that will abrade off material that will fall into block. Brass wire brush is OK but chemical works best to clean surface. Plastic scraper not metal. Finish taking off chemical with brake cleaner, not getting any down into block.
Plan on oiling tappets before re-assembling engine. Small tube of assembly lube. CALIBRATED torque wrench for head bolts (and oiled bolts).
it's possible that you have small crack in head, typically at exhaust valve seat. You may think about cleaning head and applying crack detector. Or take to shop for pressure test. In that case, more gaskets will be needed, new valve seals. Valves must go into original places, same as tappets and lift rods.
Reset valve clearance in any case after new gasket.
Lots of brake cleaner, electronic cleaner, solvent for carbon build-up, shop rags, cardboard for parts and marks-a-lot to organize parts, painters tape to mask hoses and tubes and electric connectors.
If you remove the injectors you will need new gaskets for the injectors.
Difficult to say what you will need until you look into head. If coolant leak, then you may have scale build-up. Take pictures.
Plan on having the machine down for awhile if you need to order parts, and you will.