That only applies to OEM 8 3/4" and OEM Dana 60 sure-grips with the thrust block in the center that originally used tapered wheel bearings.

If the splines are long enough, and the axles are not excessively long, you don't have to add the spacer plate.

I would trial fit the axles into the housing. Make sure both wheel bearing snap rings fit snug against the housing end before installing the brakes.