You are correct -1. is the main drive shaft that takes drive from the gearbox to the rear drive and to the front differential. This drive shaft is hollow. Drive from the front diff goes directly out to the drivers front wheel. But for the left front comes from the diff via 9 (intermediate shaft) which runs through the middle of the main drive shaft 1. into the gearbox where it connects to another shaft to take power to the front left wheel through the gearbox - I assume in the middle of the gearbox output shaft and connects onto to left drive shaft.
I am not sure your red lines in the bottom right of the IRD (Just above the .5331:1 ) is correct as the diagram does no show gears in that area and I have a suspicion the rear PTO grears do not interact with the front diff - but them who knows.
A lot of the mystery with the IRD is that drive for the front and gear is taken from at different points and at different points in the gearing. Unlike a traditional tfr case where drive to the front and rear is taken from the same point on the reduction process.
Garry

