From memory, the main difference between the
classic C-series MFD and the classic E-series is that the C-series does not have a SeaTalk-HS or RayNet interface - both of which are ethernet-based (RayNet has a water-proof connector. The RD424D radar uses SeaTalk-HS, so it won't
work. If you can find the older radar - the RD424 - that will
work with the C80
Again, this is from memory - I can't download the old C/E
manuals here at work ;-)