I ended up going with the Brown Davis 145 litre poly tank. $1319 installed. Looks like a fairly solid bit of kit.
Starting with a full tank the vehicle did 520 km before the fuel gauge needle moved, 870 km when the gauge read ½, and 1150 km until the fuel light came on. The driving conditions were approximately 500 km highway, 500 km city, and 150 km low range.
124 litres to fill the tank once the fuel light came on – so presumably 21 litres left at that point, giving a total range to empty of around 1350 km’s.
Tackled some moderate 4wd’ing around Mt Stirling – couple of easy mud holes, some bumps in the road that tested ground clearance etc. All good – never touched the tank. The bottom of the tank hangs approx. 50 mm lower than the original, but there’s other stuff to get hung up on that sits lower in some area’s. I don’t have any suspension lift, although I’m planning on upgrading suspension later in the year.