If you have a saw slit with a clamp screw which clamps the quill, you
should measure the width of the slit at a point away from the clamp
screw, towards the back of the tailstock. Whatever this dimension is,
put a shim in the slot near the mouth of the quill with that dimension,
and clamp on the shim. The hole will then be near the original size.
Now the "T" gauges will measure the hole diameter correctly. If it is
off, then bore the hole out to get parallelism and ensure EXACT center
height for the hole.

Using the new bore dimensions, make a new quill. Make the quill with
steps in this order. First bore a through hole in a piece of steel
which is the root diameter of the thread at the back of the quill.
Thread the hole to match the screw. Put an accurate, 60 degree chamfer
to match a dead center around the perimeter of the threaded hole. Turn
the quill blank around and bore the hole to the small diameter of a
dead center (2 morse taper, or three morse taper or whatever). Using
the center rest, bore the morse taper to match a test taper. If you
can get a finish reamer, use it to get the final taper perfect. Insert
a dead center in the taper, and mount the quill between this dead
center and another in the taper at the threaded end. Turn the OD to
match the hole in hole in the tailstock casting. The weapon of choice
here is a post grinder if you have one.

If you have done everything correctly,. the hole in the taper will be
concentric with the outside of the quill, and the hole in the tailstock
casting will be at center height.

brownnsharp