I have a 9" tail stock that out of horizontal alignment. I shimmed it up to the level of the headstock to line it up. Can I replace this headstock with another or are they machined to fit each indivdual machine.
Um, tailstock setover is adjustable. Do you really mean horizontal alignment? It's dead trivial, loosen the clamp bolt, loosen the setover screw on one side a little, tighten it on the other side a little, reclamp it, check it.
The best way to check it is to put a 2-collar test bar between centers and turn the outside of the two collars without touching the compound or cross-slide feed screws, then measure the diameter of the collars. If they are identical, then you're done. If the tailstock collar is bigger, then the tailstock needs to slide towards you, the operator.
It's quicker and almost as accurate to clamp a dial gage or indicator in the chuck and check the alignment of an installed center in the tailstock. It will immediately tell whether the tailstock is low or high, as well as horizontal alignment. Bugs
Assuming your centers are properly ground, I still like the crude but simple method of pinning a parallel between the centers, then adjusting the tailstock to null the offset of the piece from perpendicular. Care should be taken to get it pretty close before locking the tailstock, lest you damage either the centers or the parallel bar.
I believe you are referring to vertical rather than horizontal alignment since you say you "shimmed it up". I do not know but I suspect the tailstocks were matched to the headstock height since I have a 9" South Bend which has a thicker shim than would seem reasonable for wear correction. I have seen some instructions somewhere for building up the tailstock with permanent shims and re-aligning it. A major job should also involve the fit and alignment of the ram so that center-to-center alignment does not change with ram extension. Don Young