If you move the a-arms backward by removing the spacers, you've effectively shortened the wheelbase by the amount of spacers moved. When I was running the baby-wide mod with Slash rear arms in the front, I tried it in all three configurations: two spacers in front, one on either side, and two spacers back. The longest wheelbase was the most progressive, the shortest was the most linear. I generally preferred it in the middle, one spacer per side. Traxxas shock pistons, drilled out slightly to accomodate the hinge pins, are almost the perfect thickness.
There are no atheists in the foxholes / There is no intellect in the air / There are no scientists on the way down / Just a working example of faith versus physics. --El-P, Flyentology