Ben, I use the welded in side jacking points and pop a stand in either under the chassis rails or under the outer ends of the axle tubes.
I see no problem in actually jacking under the outer ends of the chassis tubes, they are designed to take the cars weight via the hubs anyway. It also gets the car in the air quicker because you don’t have to unload the spring first before it starts lifting the car.
It’s not recommended to use the underside of the diff although I bet many have done.
All to be done with the greatest of care of course and ensure the car is stable and well supported before venturing underneath.