Can anyone with a Wilwood kit explain this

Yeah what doesn't make sense is that the whole point of the kit is that it works on a 9" drum spindle. Why would I go through the trouble of getting a kit for a 9" drum spindle, with both bolt patterns in the kit, and then have to upgrade my wheels and tires to bbp? Wheels and tires are way more costly than just finding a 10" drum spindle from a 70-72 model. Then I would just get a kit for the 10" drum spindle, which is every other kit out there. Is Wilwood on crack?