Start with one SWB Pajero fuel tank. I think it's from a V23 but I can't be sure

and install.
It doesn't actually hang down too far, I've put the fuel syphon (small outlet) below the filler neck, the theory being that, when filling, the syphon will prime before the fuel starts to flow through the filler. It might work, but if not I can always put a pump in line. There are also a couple of 1/2" vent pipes at the top to help it fill.
All that's left to do is connect it to the middle tank. Which is the scary bit, because it'll involve cutting holes in a perfectly good tank. I might see if I can buy a spare tank first.
Full size and more pictures here:
https://photos.app.goo.gl/49xcEwtqeJGgGYwL9
https://photos.app.goo.gl/t9QPYBVrrkTC76GW8
https://photos.app.goo.gl/ZBJvU2B7QNFM9Cy76