The GGD cars are 21 inches in length. Everything they make is scale in their dimensions.
There is no comparison whatsoever between the Lionel or K line cars and GGD cars. The Lionel and K line cars are both generic cars with NYC paint on them. The GGD cars are true to the prototype in design.
GGD all the way!
But be warned... once you own a set of GGD cars, you will feel the need to sell off your other cars to buy more GGD cars! They are the very best in 3 rail scale!
Here is a video of some of my NYC cars from the first GGD run...