I assume you mean: "Is the Radom from an old RL80 system compatible with a new C series display?", right?
If so, I think the answer is some of them are. If I remember correctly, a certain range of SN#'s were compatible, and a certain range was not. In other words, at some point they made a change to the radomes that made them compaticalbe with the newer systems. Check with Ray tech support, they are pretty good at this type of question. Have your SN# from the dome ready.