Pretty much nailed it.
For 89 models:
Wider ratio box.
Stand (and mount on frame).
Lighting coil & lights.
Softer springs.
Bigger tank.
Something go different in the porting and/or PV.
Stickers.
Odometer.
Muffler for US model (not 100% on Aussie RMXes).
Later RMXes also got a different, "three stage" PV, and the stand moved to the swingarm at some stage.