The bigger issue is the lower ball joint bolts. The drum spindles used 1/2" bolts there. The KH disks used 9/16", and the later 73+ 10" drum spindles and 73+ disk spindles used 5/8" bolts.
The other major difference is the diameter of the outer wheel bearing. I believe even the 10" drum spindles use a larger outer wheel bearing than the 9" drums, and the 73+ spindles use a larger one than the 67-72 10" drums. The higher the speed you run at the more that small outer bearing can be an issue.
And on that note, just weighing the spindle wouldn't be enough, you'd need to include the lower ball joints and hardware to fully capture the weight change if you're counting ounces.