I dont know if this will help anyone, but there was a design change to the GX, which resulted in two different hitch part-numbers.
up to 4/11/04 production uses PT228-60440
Afte r 4/11/04 production uses PT228-60540
The difference that i can see is that there is a slightly different spacing one a 4 bolt flange (Tried to install an old hitch on a new vehicle, wouldnt line up; or vice verca i dont remember)
Easiest way to tell the difference between an old production GX with TO package and new production with TO package is the rear bumper insert. Old design has a much larger cut out like this one:
The new produciton TO option has a much less pronounced cutout. And i cant Find a picture of it! (would look like any '04 on a Lexus lot today tho!)
You can now get the new design hitch from Lexus without much hastle (no longer manually controlled)
Either kit does not come with the Ball Mount (or ball)
hope it helps somewhat~