What Simon said. Your best bet will be to find the fold down centre seat from the US (with seat belt) from a wrecking yard, and have it shipped. It would be easier if you could find one locally, but I am guessing it will be difficult to find.
Dropping in the bench seat by itself removes the adjust ability of the individual seats "captains chairs" as they call 'em in the US.
This is the one I have in my Super Duty, and fits with the grey cloth fitted the XLT models (which I assume are the ones you are looking at)
The hand brake fits between the dicky seat and the drivers seat (I.s. same spot as it will be on your truck). None of the Aus delivered F-trucks have a true bench seat for this reason, they are all 40/20/40 splits.
A foot operated parking brake (like US variants) doesn't meet ADR's
Good spot Patchy!
So the dicky seat is a goer handbrake wise.
On the ebay item I could see that the dicky seat had an intergrated inertia reel seat belt fitted, but I couldn't tell if the matching buckle was on the other side of the seat.
Any ideas about that - are belt and buckle integrated into the seat?
That would make mounting really easy. So easy you could swap in and out as needed!