Cat 18 Acert white smoke when accelerating in neutral

I assume the same issue before the new injectors.
Stuck or broke exhaust valve.

How old are the aftercoolers, 1 could be starting to leak...….if over 6 years, change the aftercooler.

Another idea there also.
What is happening; Either low compression or a wet with water lung is spitting raw fuel into the exhaust manifold. Some of that unburned fuel is ignited in the exhaust manifold by hot expanding exhaust gasses from other lungs.
Stick your face in that smoke and your eyes will burn if it's fuel heavy, not so bad if it's steam.

Don't mess around with this. You could drop a valve completely (if it's a valve) or bend a rod / blow the engine if water (from the A C).

If it's never been over heated
-- dock queen; valves.
-- old and good use; A C.

How old are the engines and what are the operating hours?

Do you mean ONLY in neutral? What happens under load?

Heats up things expand and the water leak self seals .......for now .

sounds like water = intercoolers are timed out service parts .

Worth checking the closed coolant levels when cold to eliminate that side .

I had C-15's that did the same when cold. When the engines warmed up the exhaust cleared. White can also be fuel in these engines, although it's a very faint white blue.

The question that was asked, regarding use and condition, is key here. Consider a cold start after a day or two benefitting from block heaters prior to start. I would think that if it was the after cooler the problem would persist no matter shutting down any injectors. Shutting down injectors will also have the computer doing backflips that will impact your effort to eliminate variables.

Watch that #1 cylinder closely. It hates heat. When she gets to temperature use a heat gun to study temp consistencies from hole to hole and along the exhaust manifold.