The gear support bracket with the oil supply tube shown at 'O' - this obviously needs to line up with the hole drilled through the casting.
The drive shaft is inserted from the rear and is fully-floating when assembly is completed.
The disc is the connection between the bearing housing and the drive shaft. It is actually a two-coil flat spring that allows slight axial displacement of the shaft. The spider is located onto the shaft by taper and key and is then locked in place by the nut.
When dismantled the three nuts and bolts holding the disc to the bearing housing were inserted the other way round but this is the correct alignment; it is a bit of a fiddle inserting the split pins.