Tracked down and fitted the correct nut to clamp the water pump drive pinion its axle.  The nut is secured with a lock tab washer.

Rear view of the water pump drive spindle with the drive coupling disk in place.

Front view of the spindle.  The castellated drive disk is located on the shaft nose by a taper and Woodruff key.  The castellations act like a constant-velocity joint: the shaft being fully floating to allow for minor axial misalignment with the water pump.

When fitting together REMEMBER to replace the coil spring over the the shaft, between the nut and front disk.

The timing cover and sump were cleaned.  Gaskets for both units were made up from masking tape.

The sump and timing covers bolted into place.  The wooden support was used to take some of the strain off the casting whilst the sump was attached.