Left work early today, and had a look underneath to see where the transmission was catching the tunnel. Surprise surprise, it was the side where FF had already fitted a packing piece under the gearbox mount. So they must have had the problem too.
They had fitted a 5mm spacer, so I created another of a further 5mm, trouble was that the gearbox mounting bolts were then too short. A rummage in my garage found a pair of longer ones, so I just needed to weld a strap across them to stop them rotating when the nuts were tightened.
That done, bolts in place and spacers fitted, gearbox re bolted back up to the mount, and near silence. It catches very occasionally, mainly over bumps, but I am leaving it for now, some sag in the mounts and it will be perfect.
The car is even nicer to drive now, transmission really quiet, a few more rattles to sort, but its getting there.
I am going to take it to work tomorrow to get another 50 miles on it, I am beginning to think again that it will make the RBRR.
And I am collecting some new S type alloys on Wednesday night - that had better fix the leaking tyre syndrome.