If you go with HDS units with the LSS-1 (down and side imaging) you can link them together. Not sure what will fit the dash of your classic, but my PIV has HDS-7 in dash and a HDS-5 on the bow. Side/Down imaging is shared through the LSS-1. Otherwords, theyre networked together. My boat had the lowrance ducers already, so I went that route, I did have to add the transducer for side/down imaging. Thats a whole nother story.