First off, what is your budget? Many options out there from $100 to north of $2k.
Yeah, if the transducer on your boat is very old at all, chances are it won't mate up to a new FF. Not saying with any certainty that it won't, just that it is unlikely. Even less so without knowing what unit was on the boat to begin with. Maybe post a pic of the connector end? Someone might be able to identify it for you.
If you're not living on the edge, you're taking up too much space!