Try Dr. Diff inboard kit which moves the springs in by about a 1/2 inch in on both sides. All you have to do is weld the spring perches in by a 1/2"
Every thing else is a bolt on.
It worked great on my stock well 65'sedan.
I run the Hoosier QTP 11.5 x 28 inch tire on a 8" rim with 5-1/2 inc h back space, no rubby ducky.