So I installed the tank, and installed a vent line to start to mimick the factory ECS system. Then I recalled due to a comment on FABO and that I needed to research the Command center vent, and I found I was right fuel would return through the vent.
Since the Command center has to be "vented" to the tank and the ESC system vents to the engine via the charcoal canister. I had to rethink things. A third line is required....more to follow and I also needed a return so I bought another fuel sending unit with a return, it arrived Friday. I checked resistance readings (73 to 10 is normal I think, I was higher) and it was favoring reading empty early which I am good with. In my Cuda with non stock exhaust I was able to swap the sender without dropping the tank (no resonators). My fuel gauge rose slightly up to the empy line with 5 gallons added from bone dry, and every 4 gallons was a 1/4 tank.

I think the return won't actually work for the vent as I'll need to vent to above the fuel level. I may need to T into one of the vent lines between the tank and fuel vapor seperator in the trunk