Well, I dug through our old manuals and I came out with one for 3Fs and one for 5Fs.
I stand corrected on a couple of things that I stated in my other posting above.
The 3F models DID NOT feature main hydraulic system boosted brakes. The 3Fs had the independent brake system like the 7F & 8F models have. So it must have been some even older 2F models that I recall having a hydraulic pressure accumulator. And I now think that the power steering on those may not have been associated with the hydraulic accumulator as those models had a sector gear box steering system with the power steering cylinder "piggy backed" onto the steering drag link. As such, the steering gear box would provide redundant steering in the absence of main hydraulic system pressure. (orbital valve with Gerotor pump provides that on more modern trucks having Full Hydraulic Power Steering systems)
Now, back to the 5F hydraulic boosted brake system.
The 5Fs DO NOT have a hydraulic pressure accumulator.
The brake (pedal) valve/master cylinder on the 5F models is capable of acting as its own redundant brake pressure source when the engine is not running (or if main hydraulic system fails), though the pedal effort required will be much greater.
And because the 5Fs have FHPS system for steering, the orbital valve has the back up in it in case of hydraulic failure.
So, now that we have better info about the components in place maybe a reason for its behavior can be determined.
There is a flow divider valve is in fact built into the main control valve that furnishes the oil supply going to the brake booster/master cylinder, but the brake booster/master cylinder also has a flow divider valve inside it (according to this manual).
Nothing that I see (thus far) in the diagrams would point to anything that might cause the engine to die with steering or brake application without some other hydraulic function also killing the engine. Will study further.
Getting back to another member mentioning "idle up" dashpot.
You say there is no idle up dashpot on this engine. The manual shows that there should be one. Furthermore, the engine IDLE RPM specs are 750 RPM with idle up vacuum hose connected and 1,250 RPM with the vacuum hose disconnected (and plugged).
If the engine is dying ONLY when it is at idle, the entire scenario may be due to the lack of a working idle up dashpot.
Does this occur only at idle or does it happen at higher RPM too?