How can I adjust wheelbase?

1.5" thick? Yeah keep dreamin.

To the OP, something is WRONG somewhere and you need to find it. Whether it's been hit and has frame damage, different length strut rods as mentioned, something assembled incorrectly......SOMETHING SOMEWHERE is amiss. Shouldn't be that hard to find as big a difference as that is.

He doesn't have to go 1.5" on the lower' I was thinking maybe 3/8" then you have to move the upper control arm back to get the caster right.