8V92 minimum compression

350 psi seems to ring a bell but confirm it. One call to dd dealer should get you the correct answer

The important thing; all lungs pop the same or close.
I like to run the motor quickly at idle cold with the gauge in the injector hole. It takes all day for two passes.
350 to 400 is very good.
Why are you asking? exhaust smoke color and history can tell more, faster?

What does the liners look like?
Bore scope the valves?
Rings loose and clean?
Both techs just embarrassed them selves if they didn't think of this?

Crank case pressures at load?
Make RPM AND speed during sea trials?

Was that turning over cold? by starter? or run a few seconds at idle?
On a 92, the coolant needs to go to the lab also.
Iron in the oil sounds like a dock queen, lots of sitting. Inside of block condensing.

Call a Dd dealer, specifically the one who marinized it and ask the service manager.

The pressures being so far apart does worry me. There is almost a 20% differential between the highest and lowest cylinder

Typical of a fuel wet lung when test like are done. Big 92 injectors dribble like a 15 year old at a kat house. That's why it takes me all day. If all was done in 4 hours, cold dry liners are not going to happen.
If they did take their time, and the engine was not run a day or two before, the valve seats never cleared and still a waist of time.
It's hard to get a good reading on old Detroits.
Now the black spots on the liners is NOT rust. Scuffing where a ring is not in good contact.
Another reason they should of been run (hard) a day or two before checking. Get those rings clear, under pressure, pushed out away from the piston.
So you really now, need to pull the air box covers off and ensure the rings are free. If so, the black spots may go away when under load.
So far, dock queen, lots of idle time, two idiot techs and old 92s.

Now, for you to think about; Are you going to idle around? Sit months on end? (idle at dock does not do anything but mess it up more).
Or you going to burn some fuel under load with a big smile and fat check book. If your worried about MPG, walk on if your worried about engine life.
There are trawlers out there that can do the same and not destroy the engines.

Not correct according to the shop manual. It is 380 at 600 rpm for a turbo engine. Average is pegged at 430.
I would have that test done again, by the way.
If not, Id run it with those numbers and not lose a minute's sleep.

Turbo engines have just a bit less compression at idle.
Still, I see no problems with those numbers. Except maybe a wet cylinder from a dribbling injector.
A visual inspection from the air box covers will be the real indicator of lung issues, ,, after a hard run..
When you see a lot of shine and no hatch patterns on those high reading lungs, Dribbling injectors or over fueling of the like. Not a big woo, Just pull all and have a good shop pop and match all injectors.
I've been preaching this for a while, picking up a set of rebuilt injectors with-out pop and match is not good service but so many do it as routine.

There were so many variables from the stock DDC to marine and different marianizers.
The important to remember; Are all the lungs the same in comparison in pressures to each other? Good looking liners?

Well, for the number techs out there; Figure 17:1 ratio at 92ci to PSI.

Not sure where the 17:1 came from, I thought my 71 TI's were 15:1.

My Detroit compression test....if they start quicky stone cold and white smoke clears quickly=OK!

Yep..

425 Psi @600 rpm