Sending unit # of ports

[eric8]

I have a 77 C10 which was equipped with the Big 10/F44 "heavy duty" emissions exemption. These had no EVAP or charcoal canister system, so I assume they came with a vented fuel cap?

Also, regarding the correct fuel sending unit on this type of emissions setup. Would the correct sending unit would be one with only one port? I know for a fact the truck did not come with a return line coming back to the tank from the fuel pump.

There are about 3-4 pages worth of fuel sending units in the parts breakdown, and i've seen 1, 2, 3, and heard of even 4 port? sending units so it's a bit confusing.