I just got back in from under the truck, outside Michigan winter!
Anyway, I have still not been able to find anything in print about the the tow bar adapters.
That's why I was just under the truck.
It has been said before that the adapter plates are for the M890. Don't have one of those, but the plates have M880 Series printed on them, not M890 Series, so I didn't believe it.
After looking this over with parts in hand,
for the 2wd drive M880 Series - the M890, M891, M892 and M893,
The plates will position the tow bar feet attaching portion under the frame rail at 34" wide and slightly forward .
refer to pic I posted in post #8 of this thread, those angled holes are what the plate attaches to.
for the 4wd M880 series,
I believe that the tow hooks are to be removed to mount the single piece adapter, kind of a narrow setup though. Holes would need to be drilled for any other location.
(I will likely use two of the 2wd plate mounting holes on the front rail and drill new holes in the second rail, mounting the adapters between the frame rail/leaf spring hangar and tow hooks, once I verify that width of the tow bar is adjustable enough for it to work there)