For a 2wd car the easiest way to mount the motor is inline with the axles. The motor has bit of effect on the car when it spools up or when you slam the brakes on, not as much as the wheels but a little. So with the motor mounted lengthways down the chassis it can have an effect on the balance / attitude in the air.
There is a car like you describe though, this photo was posted on Racechat
I dont think the car has had much testing yet ?! but looks promising.