I bought a clutch disk from Thirdgen a while ago, and it was surprisingly sloppy on the splines of the input shaft. I tried it on 2-3 other shafts I had and it wobbled maybe 3/4” or more at the outer edge of the disk. I called Michael and he said he had two suppliers and he sent me one from his other supplier. It fit a lot better, and he told me to pitch the other. So whatever you end up with, try it on your input shaft see how it fits. I don’t know that there’s a spec for looseness, but I’d never seen one with that much slop.
Now that the car is together and running, it’s the nicest clutch I’ve ever had on an old Ford.