Don't know whether this is a "best option"...but it's what I recently did when the Lowrance 3400 failed in our 1990 22' Sundancer. I installed a Faria with in-hull transducer (#12851).
The Faria gauge was smaller than the Lowrance, so I ended up taking apart the Lowrance gauge, cutting out the centre of the face so that the Faria gauge nestled inside the Lowrance face and bezel (the Faria now looks like it has a dual lipped bezel (I can photograph it if you're interested in seeing what the finished product looks like).
On the tranducer end, I tried to remove the old Lowrance transducer, but it was epoxied to the hull. I didn't want to risk delaminating by just pulling hard enough to remove it and there wasn't a lot of space to get in there and cut it out, so I just cut the wires and abandoned it in place. There was enough room to locate the Faria transducer along side. The Faria transducer had a neat approach to setting the transducer angles to match the hulls dead rise angle (I won't go into it because it's well covered in the directions.
The toughest part, I found was pulling the new tranducer wire up to the dash. I carefully peeled back the wire looms, slowly removed the old tranducer wire (often using it to pull in the new tranducer wire). I did cut the plug off the new tranducer wire to aid in pulling it into place. I then soldered it back together and covered the joints with heat shrink tubing once completed and in place.
Good luck.
