Fuel tank Sending Units

[Dukagora]

I have a 79 crew cab 454 with dual tanks.

I think I am a bit confused on the fuel system.

There is no valve to switch tanks, and I cant remember now but pretty sure the wiring isnt there. So the passenger tank was made the primary.

I dropped the drivers tank, mainly because of the substantial dent, and confirmed both tanks have a 3 port sending unit. Is this correct? Should they both have a 3 port sending units?

I have had poor experience with gauge accuracy on spectra sending units and was going with a Dorman. The Dorman I ordered is Part # 692-078. I picked it up off Autozone online and after ordering, realized I hadn't seen which side it is for specifically. Worked with the person online who really didn't seem to know a whole lot about the situation, then went in locally after trying Napa who only had spectra. Oreilly is the same way. Autozone online told me its for the "main tank" but dont know which tank is technically the main tank. I assumed the passengers side since my 77 half ton was the same way and single tank only. Then I read somewhere that 78 and 79, drivers side was primary? Summit Racing lists the same sending unit as passenger side, which wont be correct.

At the local Autozone, they seemed to believe that one side was 3 port and the other is 2 port. Does this make sense?

My understanding is 3 ports. One goes to mechanical pump, one is return line, and the other is for canister?

Pics under the hood....
Obviously left is fuel pump. Right is what looks like 2 canister. Am I supposed to have 2?

Right Canister:
Right hose goes to nowhere, but the top of canister says it should go to tank.
Left hose goes to the T in the right pic in post #2. Sorry the pics are broken up, it wouldn't let me upload all 4 at once.

Left Canister: Labeled as "Purge"
Right port is capped. says "Air"
Left ports...
Top goes down to across what I'm going to call a cross member, and routes underneath the mechanical pump and goes back to the passenger tank.
Bottom goes to the drivers valve cover into a 2 port, I am guessing here, PCV valve. Top port on that PCV valve. Once you rotate your head 180 degrees, you can see it in the pic in post #2.