I'm not saying this is correct but years ago when I thought I was going to have to drill a flywheel for a 360 this is what I thought I saw:

1) establish the horizontal centerline through the pressure plate holes
2) establish the vertical centerline 90 degrees from the horizontal centerline through the center
3) establish the centerline of the middle hole by rotating 46 degrees 21 minutes clockwise from the vertical centerline through the center
4) establish the centers of the two outside holes by measuring 2.5 inches from the center hole at the 3.88 inch radius of the balance holes

Like I say, I never had to do this (found a flywheel) but this is the way I would have done it.