All right, let me try to explain...
Our cranks have nine bolts for attaching the flywheel. They are spaced around the crank flange as if there were to be ten. Instead of a tenth bolt there is a blank area on the crank flange, and a small hole in the flywheel.
If you measure the flywheel run-out on a high mileage IDI it will almost always exceed the .008" allowed by ford even if the flywheel is true. If you measure the run-out of the crank flange you will find they are out by several thousandth's. If you measure the thickness of the crank flange (on a used crank) you will almost always find that the blank area (where the 10th hole would go) will be several thousandth's thicker then the opposite side of the crank. If you have a "grabby" clutch even after a new clutch assembly & flywheel this is likely your culprit.
Unfortunately most crank shops don't even measure this flange, let alone reface it. They simply assume it has to be OK if the crank is straight. I have found this not to be the case. Both my old crank and the reman I ordered displayed this very same run-out. Even though both cranks are perfectly straight. I even had the reman balanced a within a gram. The guy who balanced it told me there is no way he could balance the crank if it were not straight.
I believe that the unequal pressure applied by the flywheel bolts, combined with the temperature variation, vibration, and possibly corrosion; causes a dimensional change in the thickness of the crank flange. This creates a thick spot exactly where the "10th" bolt would be.
Make any sense?