Between my bearing carriers and drum plates there are 3 shims out of 0.1 mm aluminium beer can foil, and one out of 1 mm ali sheet, tapered a bit with a hammer
That's how you tune rear toe on these things. I've set mine to about 0.5 degree toe in. I measure it by clamping a long spirit level ot just a straight piece of chassis tube to the rear hub face with the drum off. Then just measure the difference of the distance from the side chassis rail over 80 cm from the rear of the cockpit to the start of taper. Some simple trig: sin(x) ~= x for small angles (in radians). If you get, say, 2 mm difference at 80 cm away, you have:
2 / 800 * 180 / 3.14 = 0.14°,
or 8'36" toe in at that wheel.
The book recommends 0 rear toe, but I've seen that Westfield World recommends 0.5-1 degree toe in both rear and front. So I've set it up with a bit or rear toe now.
P.S. One beer can shim corrects the angle by about 4'.