Diesel 6-71

You should easily see flaps at the airboxes, attached to a cable. Hard to explain but pretty obvious when you see them

Stright or Natural 671 (671M) usually did not have shut down flappers.
1950, I doubt it.
In case of an upgrade, I'll proceed;
671 T, TI & TIBs (anything with a turbo) did.
Find a Morse cable that looks like a throttle or clutch control cable, but is not,, Connecting to the engines side above the blower (super charger).
Here at this vertical cable end is a pull to release (spring loaded) cam that closes an internal flapper (closing air off from the engine).
Should be a lil lever that you can push with your thumb. With the shutdown cable (in the wheel house), push on this lil lever till you feel or hear a click. It should now be locked open.

There may be a horizontal cable above all this, this is your throttle. Don't mess with it.

If you can not still find it, Take pictures and post them of both ends of the blower.
We will figure it out for you.

I looked over pictures sent.
It is an original 6-71 without blower shut down flapper.
I'll resize the pictures and post below in a few minutes.

Any long set of numbers that start with 51 is a later part number.
5167294 is the water manifold part number.

That is the later head, water manifold, valve cover and exhaust manifold.
I can not tell if that is the 2 or 4 valve head.

Further, I do not see any shut down system attached to the governor top either.

Original GM/Allison M clutch.

Sweet ole girl needs a new dress.
I'd say most of that rust is from condensation. When was the last time she ran and under load?

Keel cooled? Raw water pump just goes to a later exhaust dump can.

With the un-original idle set screw, I would say throttle all back kills the engine.
Open the throttle some and try to start her.

Here they come;

That MDJE and water heater in the back ground could make for great reef material.
Could that gen-set still run?

Where you at?
Closest big town / airport?
If it's a Detroit and spins over, we can make her run.
No promises how well.....

Frack, It had to be Norfolk.

Try my first idea (open throttle and crank to start) first. If no joy give me a ring.

Yep, That is the governor kill lever, Nothing attached to it. When pulled on, it over rides the governor and pulls the racks to no-fuel and the engine dies.
It also has a nice spring action to return to the run position.