Is there a reason you can't just write the data from the ControlLogix?
I have not tried that. My main concern there is if I have a write failure too many times, it may cause a fault in the L73 controller which could affect all of my control systems (pretty much all inclusive) in my utilities plant. I am not sure of what a write failure would do in my primary system (L73 processor). IF I have read failures in the secondary system (L19ER processor) and it causes a fault, it only affects a single system.
I may give that a try and see how it goes.