This is a prop-shaft. It connects the engine to the differential and runs through the centre of the car.
Fitting the prop-shaft is simply a case of bolting one end to the diff.
This is done with special fine threaded bolts which are apparently difficult to get hold of. These are bolted in place with a bit of thread-lock to stop them shaking loose.
The other end is bolted to the sprocket adaptor on the engine.
This is done with bolts that go through the prop-shaft end, and through the sprocket adaptor. These are then secured with some nylocks.
The central bearing carrier kind of finds it’s own final position. IT is then bolted to the chassis in the transmission tunnel.
But mine did not work out like that. The prop-shaft was fractionally too long which meant that the shaft didn’t sit in the tunnel correctly such that the it was rubbing on one of the chassis rails when rotated. So it had to come off and I will need to consult with MAC#1 as to what to do next.