suggestions for upgrading headlights on LS400

I believe that the shape of the headlights for the LS 430 and LS 400 are different so they are not interchangeable.

What do you mean by "upgrading?" If you have halogen headlights, you can install high intensity discharge lights from the same model year, although by the time you get the headlight assembly, wiring harness, and ballast, you will probably spend in the neighborhood of $2,000.