This is an old thread for the Ford/Long 10-inch flywheel drilling dimensions so a person can get an idea of how to go about it.
https://www.fordbarn.com/forum/showt...4069&showall=1
The 9-inch clutch is on a 10.375" circle so that can be divided by 2 to get the radius for the centerline to hole distance. It will be 120 degrees between the first holes and should be 32 degrees between pairs. The distance between pair centers is approximately 2.830" if I remember correctly. A person can use a DRO if they have one or a rotary index table. It just depends on what a person has available to them. It should also be noted about where the original set of holes is so that they can be spaced evenly apart enough to prevent weakening the flywheel. Hole sizes and thread per inch should reflect the size of the cover bolts that will be used.