'.... in addition to the new Sea Searcher radar and TANS.'
You're right - I'd forgotten about the Mk5's new TANS (TANS G?) I recall that it was significantly better than the Mk2's - even without radar integration. However, there was one drawback. If I remember rightly, it incorporated a new doppler system (Doppler 91?). Unlike the Mk2's doppler, the Mk5's didn't provide a direct height read-out for the pilots. This facility was a useful backup to the Sea King’s (single) radar altimeter, and its loss was a distinct retrograde step.