I did this using a lathe but only needed to shorten them a 1/8". I left the cup end in the pushrod and used a parting tool bit to machine an 1/8" off the pushrod till I reached the cup insert peg then pressed the cup further in. Worked fine but if you need to shorten them a lot you would have to check how deep the holes for the pushrod ends were drilled so you do not bottom out trying to press the ends in after you have shortened them.
Good Luck