That sounds reasonable. I didn't see much of a register on the chuck itself I have both of the 3 jaws, and I'm using the small one on the Levin, and the large one with a 3C shank in the Southbend.
I'm considering facing back the adapters just a touch to make a register, and then boring the same into the chucks to improve repeatability.....but I've not actually measured anything yet.
Dave