Gas tank vent tube

[Firebirdjones]

One of those larger connections that appear to be either 1/2" or 5/8" is probably meant for the overflow tube that connects to your filler neck. Mine has an overflow tube (or filler vent) that connects to the top of the filler neck and it's about that size.

So you have your fuel supply and return, possibly an extra filler neck tube of 1/2" or 5/8", then you can use the other small tube coming out of the sending unit (which appears to be 1/4") for a vent hose if you wish (so you are venting at the very top of the tank), or use a vented gas cap since you don't wish to use the charcoal cannister.

The rest would simply be capped off. That's how I have mine setup running a 6.0 LS engine. Works excellent.