I have the older plastic header tank in my model IV. The low fuel sensor does fit in a port in the top of the tank. I have one installed. I have had trouble with some leaking around the various fittings of this tank. A few years ago, I removed the tank, removed all of the fittings, cleaned the threads and reinstalled everything with a two part polyurethane sealant. One version of this is trade named "Proseal". No leaks since.
At the time I was told that the aluminum header tank solved the problem with sealing around fittings but that I would lose the ability to have the low fuel light so I went the proseal route.