Not going to read through that ad again, but from memory I seem to remember it saying that it had a datsun tranny. It definately wasn't a standard transmission, hence the different boot.
I'd suggest you remove the metal housing (it's just some allen key bolts if I remember right), measure the hole underneath and take a wander down the scrap yard.
That said, I think the top of the gearbox may sit slightly proud of the tunnel, hence the metal bulb covering.