I'm not even sure it will be a 50/50 split if you weld the planet gears. But even if it would, the front and rear propshaft cannot turn at a different rate anymore because you welded that part. The viscous is normally slowing the difference between the turning rates, but if it's welded the viscous doesn't do anything anymore. With the front and rear propshafts only being able to turn at the same rate the car will only go straight.