I finally got around to installing my 99 upper and lower gates. The upper went in with no problems. All harnesses matched and the trim as well.
Where things ended was when trying to install the 99 LC lower to my 00 LX. First, the wire loom exits the 99 on the passenger side to the car and has a totally different plug style vs the 00LX which exits on the driver side. The inner taillights are completely different on the 99 LC tailgate as well, with no chance of swapping over the lights from my truck. Different shape, different cutouts in the sheet metal.
I ended up keeping my original tail gate in place after realizing that the rust raining down was the clips that hold the LX cladding to the gate, and not the actual sheet metal of the gate. So i just cleaned up the adhesive and rusted clips and stuck the cladding back on with 3M body tape.