That seems like it would work if you can find measuring spots on each side of the chassis that are totally equal, then find the exact centerline of the other end. Your chassis would have to be perfect as small deviations can make big differences. I use a set of $300 modified ruggles style scales that work pretty darn well, although they are a little harder to level accurately. This dude makes them.
http://motors.shop.ebay.com/merchant/sprintracerman