Different front and rear track

Spacers are not a good idea as will knock hell out of your wheel bearings..Also if the front of the car is book width and the cockpit is wider the car will look odd in my opinion...any nosecone you buy will look odd as the angles are all wrong.

Why don't you just make the whole chassis wider and adjust you suspension to suit, at least that way you create a "new car" and one that won't look so weird.

All my own opinion but based on playing with these type of cars over the last few years....skinny 7's look better than fat ones