in order to get the true scale youd have to do it by hieght or the headlights as they mess these bodies up to make them cartoony.. i did the same thing
lol im trying to do it by width as i dont think they changed much of that to scale as the hieght or length... i did the math for the track i got 20.5 ft add another 3 or so feet for the run down @ the end and the stageing area.. would be sweet..