Does the chuck normally attach to a backing plate with bolts through from the front or does it have tapped mounting holes at the back?
If it bolts from the front can you put bolts through into tee nuts in the slots on the rotary? Then just dial it true.
If it has tapped mounting holes and is the same size as the rotary you have a problem, but if the chuck is smaller you can make a mounting plat that bolts onto the chuck and extends post the chuck OD and then attach this to the rotary with bolts and tee nuts.
Or you can take my approach if the chuck is the same size and drill mounting holes through the chuck body and bolt it from the front. Certainly not recommended if you plan on using the chuck in a lathe at any time.