You do have to remove a little material from under the saddle to give
clearance for the ballnut. I just used and angle grinder.
Here's a pictorial that hopefully explains it. I didn't take any pics of the before
and after, but was able to compile something close. Hope this helps.
Also have a high res .zip of the drawing and the ballnut stop blocks rev B.dxf
that shows changes I made to the X Axis block to give more clearance.