they use the spacer to bring the hub bearings out 1/4"?
This is when you use the XJ hub bearing in place of the WJ bearing.
I know why you use the XJ bearing to keep the same 4.5" bolt pattern but what if you wish to use the WJ's 5" bolt pattern. I can easily drill out my 8.25 axles to the 5" bolt pattern and use the WJ's rotors on my rear discs and not have to get a plate and add a spacer for the caliper bracket etc.
Unless I'm missing something else.

 

No, you miss nothing.


I'm going to use the WJ bearing unit as I have dual pattern wheels. Rear will remain 4.5x5.


For that matter, if the disc has the same set back/spacing, you can order new dual pattern rear axles and just move to 5x5 all around.......they are not that expensive.

 

The XJ stub axle is too short to insert the cotter pin when using the WJ unit bearing.

Using the WJ stub axle in the WJ unit bearing fits but it is set up for CV and not U joint.