here although I will share what I once watched. It also was on a Yanmah.
The instruction was to remove/loosen those things related to the injector. DO NOT REMOVE what I will call a keeper. On the engine
I saw, there was something protecting the injector from flying out. Very important not to remove it, could cause great injury if removed.
Next, turn the engine
over. NOt sure if this was by hand and that engine had a hand crank. Been too long to provide details. The compression
would pop out the injector.
More important things----never put any part of you body in line with the injector's nozzle. The pressure is very high, you will need a trip to a hospital if fuel oil
gets injected into your skin.
Here again, a little knowledge can be dangerous so be careful and I ain't no mechanic
so keep anything in this post in that " I ain't........." light.
One final comment from my know nothing experience. Black soot may or may not be caused by injectors. I once had mucho black soot poring out the exhaust
. Problem was a DIRTY INPUT AIR FILTER!!! Hope you pulled that head for the right reason and good luck.
EDIT: Your pictures appear to show a bad head gasket