Acceptable Wheel Offset Front to Rear

[Joaquin Suave]

Now that I have decided the use A3 rims for my Conti 365/80 R20 Tires On Casa Azul, I now have the dilemma of the rear wheels (offset facing outward) being 4.5" more narrow than the fronts (offset facing inward)...
That seems too much to me, so I am planning on machining 2 offset spacers 1.25" thick. That way the width difference would only be 2 inches.
Anyone care to give me some advice???