I have dual tanks with a single fill on my '74 Cherokee. I also have the tank selector on the floor but mine has a toggle switch on the dash to see how much fuel is in each tank. I believe the original owner added that but maybe not.
The selector works on mine. Actually ran the one tank empty and switched it to the other and all was well.
Probably didn't help you any
Now I do need to figure out the vent line routing for them. I filled both tanks once and when it got close to full, fuel started pouring out of a line. But dropping both tanks does not sound like fun.