EquipmentAsOldAsMe

I have been doing some research on data highway and data highway plus, and have contacted Allen Bradley for information regarding communication. We are currently working on a project that involves us upgrading a clients PLC from a PLC 5 to an L81E processor, I have run into an issue where the old programs destination node is larger then 77 which wont be accepted into a new message instruction. I believe this to be addressing a DH connection that I read has a different node addressing system. The customer would like to keep the same network so we were considering using a 1756 DHRIO card to communicate on the DH+ network. Has anyone had experience in this and can steer me in the right direction. Thanks