That should be about right. You won't have much shrinkage, maybe 20% tops depending on cook temps.
We used to cook 12 ribs a day in an Alto-Sham rib oven, which is remarkably close to a CS in function, and also very moist. We weighed every rib both pre and post cook, and IIRC averaged maybe 12% loss. Have a great party. Sounds like it will be tasty.