If it's an open diff, you'll see the side of the cross pin/shaft when you look into through the opening that the axle shaft is inserted through.
With a Torsen there is a spacer plug in the center, so when you look though, the view will be blocked except for a 3/8" or so hole that is in the center of the plug.
I can't speak for the Quaife though, but a previous post suggested it might be clear all the way through the opening.
