I looked into this a while back for my sedan but couldn't find anything.
I ended up getting a flexible bladder tank and plumbing it in to the factory filler, all gravity fed and drained with a breather out the top, I've recently taken it out so I can get LPG in.
I took photos as I removed it, so I'll post a guide of what I did when I get time.
Back on topic....
http://www.browndavis.com.au/tanks.php?make=FORD&model=FALCON&series=2002-2009
These guys make a 132L tank that goes into the Utes.
It fits in perfectly, uses the factory hoses, fuel pump, gauge etc. Its just a bigger capacity tank.
Reasonable price too. You can pretty much fit it yourself.