The other 4x4 gearbox is a type 9 box, this was fitted to all 4wd mk1 sierras,
Mk2 sierras have the mt75

The split is 36-64

If you turn the gearbox round like your saying you would be drive the rear wheels with the little transfer box output, would be a bit shit really!

With regards to how much power they can take ,
I have yet to kill mine in 4 years of hard launches and 2 clutches ,
I've killed my ap 6-paddle clutch plate, pressure plate and flywheel and the gearbox is still fine.
Been drag racing few times this year and always full bore launch it 5000-5500k
Car is running approx 330bhp