Trutrac 8 3/4 Axle Spacer

Finally got my rearend back from the shop (741 w/ 3.23 and trutrac dif) and have a question setting axle end play. The dif came with a steel spacer, so does this just float between the internal ends of the axles? Reason I ask is that the open dif has a rectangular block fixed in place. If it floats what is the easiest way to set endplay since one side relies on the other?

I am using the factory cone bearings.