yeah on researching as @ballywannabe stated there are difference between them:

the very early Stern's tombstones had no hood, then around the early 80's went to a hood variety but hooded front and back as well to the sides and bally's were hooded front and back and though are the same length the bottom pivot hole is in a different location and sections of the target are the same but there are differences at the top and bottom.

as for the guy that asked me, he is a aussie collector of classic sterns and paid a company to replicate the target but they did a crappy unusable 3d scan and a through away. So I donated my time to replicate to help him and other purists restore their games to the early intended design. I will find out what games he has that he intends to install these into.