yea, it makes a difference.

using the front pullback wheels on the front of your bit without spacers would cause it to rub on the chassis. it would do this because you could push the pin in so far (so you don't get that "flop" Murcielago is talking about) that it would cause the rims to rub on the steering arm and then the tires would rub on the chassis.

if you use the rear pullback wheels for the front, you can just keep the spacers on the rear pullback wheels as they come and slap them on the front of your car and then all you need to do is trim down the front wheel wells of a body just a bit.