OK, back on track. Walked over the shed with the casing and pressend out the main bottom bearing.

There is a thin circular plate held on by 4 tiny screws that has to come off first. The bearing and seal is oriented like this.

Then moved onto striping the bottom section of the head, starting with what I think is the idler gear.

Then the bushing that the pinion shaft sits in (IIRC
)

And the feed disengagement shaft/pinion

Removed the clutch box cover

Close up view showing location of circlips and pins

Removing the gear from the pinion shaft

Revealing another circlip on the shaft itself, hence why you wouldn't be able to remove the shaft without coming in from the clutch end.

Shaft removed

View inside the clutch cover showing how the clutch lever is located

And finally, removed the worm shaft from the head/overarm

Thats the head pretty much stripped now.
Might move onto cleaning, painting and stuff like that next so I can get some of this re-assembled before I loose any parts or forget how they go together 
Cheers,
Paul.