Thanks OneownerT. I haven't been able to find a vehicle with the BW4472 under it to see what the dimensions are like. From what I've seen on the web, it would be a lot easier to fit. Even better, they're relatively plentiful and inexpensive compared to other cases. I haven't ruled it out.
However, I've also been thinking about the larger 4473 or NVG 149 which are used on the FS truck chassis with AWD. They have presumably a higher torque capacity than the 4472.
I haven't been able to find ratings for the 4472, but its been superceded by the NVG 126/136 on Bravadas and Astros which have torque ratings of around 1500 ft-lb. The NVG 149 has a 2200 ft-lb rating and a magnesium case. The 149 is largely in trucks while the 4473 is largely in vans. Problem is the shafts are spaced much wider apart than the 4472 - between 50% and 100% the distance from what I can gather.
I figure if I'm going to go through the work, it would be better to try to make the heavier, although larger, case work, if possible.
One thing I've noticed though, the 149 has mostly empty space in between the shafts - possibly to use the same space as a standard FS truck 4X4 xfer case. Perhaps it would be possible to swap the higher capacity parts from the 149 into the 4472 with a smaller diameter belt. I suspect the viscous clutch is the main failure component, probably followed by the belt.