When doing head gasket replacements on these engines a few things to consider are:
1. The injector lines are considered to be a single use item due to the injection pressures generated by the common rail pump- reusing them may result in a fuel leak & risk of engine bay fire
2. Each head gasket has a letter assigned to it which indicates the thickness of the head gasket - one needs to know the letter or know how to measure the gaskets thickness when ordering so you get the correct gaskets - parts would need to come from RockAutohttps://www.rockauto.com/en/catalog/jeep,2015,grand+cherokee,3.0l+v6+diesel+turbocharg ed,3309741,engine,cylinder+head+gasket,5412
3. One would also need to check if the head bolts are single use throw away jobs which need to be replaced as a stretched head bolt will result in another blown head gasket(s) & whether or not the heads have been softened/warped by overheating (specialist engine cylinder head repair shop).
The electronic repair manuals would need to be read over a couple of times to check for specialist tools for timing the camshafts, torque wrench settings etc. It may also be worth giving these guys a call
http://allgrandcherokee.com.au/
to see what they recommend ie: repair existing engine or fit a low mileage complete second hand engine & use your old engine for parts etc.
Cheers