We have some 1.5mm aluminum front shims and some 2.5mm rear shims. These in conjunction with the thicker OEM shims, we usually find a combination that works.
However, with the adjustable perches - lowering the front about .75" and the rear ~1" will typically put the GT in aggressive-street set-up with the potential of camber in the rear being just a tad aggressive. However, noting that 95% of GT owners tires are replace on age and not wear, the rear camber is mostly a don't care.