Its a fundamental difference in the entire exhaust system.
The basics are to keep the water from getting back into the engine.
The original system looks like it does that well because the water being injected has to get back over that 3ft high dry loop.
Additionally, if you crank the engine for extended periods of time with out it starting (like when you bleed the fuel system) you will not risk flooding the engine.
If you end up with an engine like the new one in the picture, and its water injected elbow off the manifold, it would normally be followed with a water lift/water lock at least 12 inches from the bottom of the engines heat exchanger exhaust opening to the top of the water lift.
I would consider your present exhaust layout as being better…and it may be possible to remove the injection elbow or not have it included (you pay for it) and assemble your original style system.
One thing I would consider is to delete the heat exchanger for the water heater, and replace it with a piece of SS exhaust pipe.
You would normally use the coolant in the engine, not the sea water, to circulate through the water heater.
The new engine may already have an outlet and inlet for this purpose.
I’ll try and attach a drawing that shows two of the most common scenarios…. unfortunately the one you presently have is not show but in my opinion is still the best in you situation.
S/V Arctic Lady