I have a 1976 280z.  This was the gas tank that was installed.  I pulled it out to install an fbody plastic tank for my LS swap.  I know there was a difference between early and late 280z tanks.  Can anyone tell me how to confirm which tank this is?  Also what would something like this be worth?  It's in great shape.

Looks like a '75 - '76 tank.  Check to see if there is a round tube inside as a baffle.  The late '74 tank is the same, but without the round baffle.

Take some pictures through the fill hole to show how much rust is in there.  Should be worth a lot.  The tanks changed in 1977, so 75 through 76 would be right.  Looks like the original 76 tank.

If It helps, I have this same tank in a ‘77 UK 260Z!

If you don’t need it and it’s in good condition, it would be of interest to me.

Here is a picture from inside the tank

Yep, super clean inside.  It's definitely a FI tank with the baffle tube as well.  That should be worth some $$

That looks in excellent shape.  The gauge sender also, which is also big money (sorry AK260...).

Here are some comparables.  And, probably not really available if a person tried to buy one.

Make sure you keep the filler cap also.  Those are NLA everywhere and anywhere.  Impossible to find.

https://zcarsource.com/fuel-systems/gas-tanks-components/gas-tank/

Why did you need to switch tanks for the LS swap? Thats an EFI tank. Are the lines not large enough?

I prefer an in-tank pump