So I am either not using the multimeter correctly, or the resistor is not working. All I get is a 1 not matter what. Same as if thr probes are not touching anything.

The resistor was bad see the broken metal arm?

So I took the sending unit off of the new 1989 low pressure assembly and put it on the old high pressure pump. I read between 16 and like 160 (or something high) ohms.

Not a direct replacement, but at least the gauge will read.

That "last spot" is the ground connection for your Fuel Gauge Sending unit, the ground path is the metal frame parts that the resistor box is mounted to.
You most likely have a black wire on your connector for the gauge ground.
The pump ground is usually Orange.

i did not see a part number anywhere on the one the original high pressure pump. Here is the napa part number for the low pressure one that I snagged the sending unit from C-0025-H

Oh and it was a success so far. Truck idles and revs well. And the gauge is reading just below full, which is good since I know there is at least 15 gallons or so in there.

Now to decide if I tackle the pump in the rear tank tonight or not.

Thanks everyone for the help and support.