I went through this as well. For all measuring, you need to be consistent. I used the face of the bell housing as the reference point for all dimensions.
Once you pull the tranny, measure the distance from the hub of the clutch to the bell housing face. Then give yourself 1/4"-3/16" for clutch disk travel, (i.e. subtract that amount from the previous dimension). Then grind your spline and use one of your disks and put it on the spline. Make sure that, when pushed all the way on the spline, the dimension between the hub of the disk and the mounting surface of the tranny, (which will end up at the same point as the bell housing surface)does not exceed the allowable dimension that you have previously determined. I had to keep grinding bit by bit until I had more than enough clearance, since I didn't want to hoist the tranny in any more than I had to.
All works great.
