Exactly. 2.5L 4 cylinders and some early 4.0L 6 cylinders have 21 spline inputs. Later 4.0 "usually" are 23 spline. In addition: every single transmission offered had a different input shaft length.
Aw4, nv3550, ax5, ax15, nsg370, etc... Some can but cut shorter but none can be cut longer...