Andrew,
your set up looks normal. You may want to try pink rears instead of magenta for low grip and yellow rears instead of grey once the grip comes up.
You may also want to try removing the shims behind the front wheels and spacing out the lower a-arm instead. Shimming the wheel makes the jacking effect due to caster more pronouced which can lift the inside causing snap oversteer you describe. Widening the car at the lower a-arm doesn't do that. You may have to place shims between the front wheel and nut to take up the slack.
Good luck,
Etienne