I don't know if original alloy rims from a 91 LS400 will fit your 98, but i've got 4 already mounted with Blizzak snow tires used only 1 short season that are taking up space in my garage. Tires were sold by my Lexus dealer and recommended for the LS400 - 225/55 R16. If you're interested, email me at tseute@cox.net and I can send you pictures...
Tim