Nice to see it all laid out like this. First we have an overview of viscous coupling installed driveline. This has both rear and front differential locks.
Another view of same.
And here we have the much much rarer version. No viscous coupling, where it was is now a straight shaft. Power to front is now controlled by a de-coupler housed in nose cone of transmission.
And here is cross section of the front differential, showing viscous coupling install.
And a cross section of the rear differential and transmission.
shooftie 