[Pete]

Any spacer is no different than bolting the spring to a flat plate as in suicide front perch.
The bolts hold the spring in place, The radius rods/wishbone keeps the spring from twisting.

For what it is worth, the SCTA at Bonneville never even commented on my 2 inch spacer bolted to a flat plate.

As a last resort you could have the spring re-heat treated and re-arched. That probably won't gain you 2 inches though.