What is the point of doing a "plus five" 20 inch wheel setup on a 90-92 gen 1 LS400 designed for 15 inch wheels? Are you trying to set some sort of record?
It was not many years ago that a "plus three" 18 inch setup on a 90-92 LS400 was considered to be completely extreme and "over the top." But a "plus five"?
Suggestions? Get reasonable size wheels and tires.
But, it looks so cool. :P
Seriously, 20" wheels on an LS400 look like pure !Removed!, especially when done the typical way of just bolting them on without any changes as it raises to car to near 4x4 status. Not to mention the rolling diameter effectively changes the gearing and the added weight makes the car a !Removed! to drive. A properly lowered car on correct size wheels (18" is fine) looks light years better, rides better, and can still accurately display the speed it's really going.
I'll never understand the desire to make a car look like a Tonka toy.