Can anyone give me a logical or simple answer as to the fluid level in the rear end? Something like fill it till it runs out of the bottom of the fill hole?

Later axles with the fill hole below the centerline of the axle - fill until it runs out of the bottom of the fill hole.

Earlier axles with the fill hole level with the centerline of the axle - fill until your finger goes into the fluid just enough that can tell it's there.

Doesn't need to be precise as long as a reasonable amount is there but well below the centerline. As soon as you start driving the oil is thrown around and well distributed. Too high and it will try to run out the axle tubes.

The correct amount is one pound, which also happens to be one pint.