Tytus,
That is a very useful implementation of the crab, because it allows for a separate gearbox that can shift and doesn't have to rotate with the wheel. Matt R. is right about the simplicity and here is a cross section of our 2003 crab design:
2003 Crab module cross-section
It requires no welding and uses a moment carrying bearing to take the entire load. We have used this bearing for 2 years now.
You can actually take your differential transmission and couple it with your crab module and have a pseudo-CVT with crab steering.
Thanks for sparking the discussions with your inventive designs.
-Paul