Shortened 8.75?

With the spacer inside the center section, they will center up. Install the drivers side first without the adjuster, and then back off the adjuster to about 2 turns from falling out. Then install it on the passenger side. Slide it all the way in, secure the retainer gently and check for end-play as you go. If you have end-play all the way, adjust it out until you are near zero, then back it off two or three turns. Now go over to the drivers side and push that axle in hard. If it moves then the center spacer is not bound up. Install and torque all the nuts; then Go back to the adjuster side, push it back in,(see note 1) install the nuts, and reset the endplay to .007 max, .002 minimum, and you are golden.
note 1
If when you attempted to push the axle back in on the adjuster side, and it did not move; then STOP!, it is bound up on the center spacer, hitting the crosspin, and either the drivers side axle is too short, or the adjuster side is too long, or the axle housing is offset to one side. If this happens to you, swap the axles side for side and start all over.
BTW, your backing plates will have to be installed prior to all this, with all the gaskets.

If it turns out one axle is in fact too short, don't panic! Just determine how much longer it needs to be, then weld a washer onto the end.

If it turns out that one side is in fact too long, You have a choice; to cut some off and dress the splines or fabricate a spacer to fit between the backing plate and the housing.

the center spacer has a very wide range of "float". You could adjust it's width to solve your problems, but that is a PITA to take it all apart.

If you have a Trac-Loc type of SureGrip with friction clutches; they have very tiny Thrust buttons which are very easy to lose. Make sure before you install the center section, that the buttons are in there.