In the Ironworking industry I know that the engineering standard is to have room, outside the threaded hole for half the diameter. Thats a 1/4" -28 threaded hole in the tang, so if your were to cut the tang off somewhat, and you were using the hole, I would leave at minimum, 1/8" behind the hole.
Paul
Doing a quick measurement on a 40X I have here, I have approx. 3/8" behind the hole... So cutting approx. 1/4" off should not be a problem. Remember the hole is as large as the major diameter of the threads, so if you do this and you are setting up in the mill, go 1/4" behind the center of the hole.