Before drilling and in some cases tapping the holes in the beds, the 9", 10" and 12" Atlas built beds with 3/8" ways are all the same. So two 10" or two 12" tailstocks will fit any Atlas made bed except those for the 6". The same 10D-6 Tailstock Base is used on the 10D and later and the 101.07361 and 101.07381 and later except for the 12" lever operated tailstock and the 12" tailstock turret (they both have 2" high bases). We have no parts lists for the earlier 10" or for the 101.07360 and 101.07380 but presumably they all used 10-6, which would probably also fit all of the beds. And for that matter, aside from having to adjust the clamp bolt length, all of the tailstocks will also fit onto the late 12" 1/2" beds. I have had both the 10D-6 and the 2" tall version of the 10D-6 base (L6-6A) on my 3996.
The front to back position of all of the Atlas tailstocks is adjustable. So although it won't much matter with a bench center, you could temporarily fit a carriage to the bed and match up the front to back positions of the normal and turned-around tailstock.
Also, the tailstocks are within 0.005" of being bilaterally symetrical. And have approximately the same offset capability (if you put the same slotted head adjust screw in the rear as in the front) in both directions. So pick either one as being correct and adjust the other one to it.