Ok, so I did a little internet research. There are different kits for the Magnumforce spindle (140-11547) and the stock 73+ disk spindle (140-15468). The only difference between those kits is the caliper brackets and the caliper bracket bolts. It's right in the part #'s listed for the kits, and you can even see a difference in the brackets in the pictures on Wilwood's website.
Now, WHY is there a difference? Not sure. I would guess that the Magnumforce spindle is a little thinner where the caliper brackets mount, and based on the picture maybe the caliper bracket mounting location is slightly different. It's not enough of a difference to cause problems for the stock disks, the factory tolerances are fairly loose and the stock calipers are floating. Which means a small difference in the position of the caliper bracket isn't a big deal, it can be absorbed by the distance the caliper can float as long as it's not too far out of whack. The Wilwoods are fixed calipers, so, if Wilwood didn't give themselves enough room then a small change in the caliper bracket location could cause interference. So, two different kits with different caliper brackets.
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140-15468
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140-11547
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