What type of lube does a manual steering box take? Service manual states not to use gear oil.

There is gear oil... and there is GEAR oil.
Transmissions also use a gear oil.
The Rear axle uses a special type of "Hypoid" lube that has friction modifiers.
They all look similar but have different additives. Manual transmissions should't use the Hypoid axle lube because the additives in it cause trouble with the synchronizers.
The short answer is to call Flaming River. They make new manual steering boxes and should have an answer for what is applicable in the older manual gear chucks.

They were packed with a grease from the factory. I can't remember the spec for it, however. Maybe a good long fiber stiff grease would work. ?

The original lube that Mopar called "steering gear grease" is actually a really heavy fluid (600 weight), regular chassis grease is recommended to top off only if the correct lube isn't available.

The article you refer to used a combo of chassis grease and 90 wt oil which needs to be heated to flow, the original heavy oil flows at room temperature.

Mac's Auto Parts in Lockport, NY has the correct 600 wt steering box lube.