I have a '98 and did the same thing you did putting in an LCD so I needed a new backup monitor. If yours is similar to mine, and I think it is, it's not as simple as plugging in a new monitor via RCA plug. The old system has a proprietory "funky" connector. I ended up buying a cheap 7" monitor with an articulating arm and mounted it underneath the old TV cabinet towards the left side of the cockpit. I had to splice into the cable for power, etc. If you swapped out your old TV I bet you could do this as well.
1998 36' FDS