I retrieved one of my K-Line AFT Display Cars from storage and compared it to the Lionel car and to the prototype car. To start, here is a photo of the prototype car.
Now below is a photo of the Lionel car on top and the K-line car on bottom. The pictures are off color; both cars are very white and the red and blue match very well between the two cars. AMERICAN FREEDOM TRAIN is not correct on either car, but both look good. The Lionel car has the Kinematic couplers while K-Line's are attached to the truck. It looks like the K-Line cars will be closer coupled than the Lionel cars.
And the winner is.......well, that depends on what you are looking for. Lets start out with the car itself. Below we can see that the Lionel is a bit longer, while....
the K-Line is a bit wider.
The most noticeable differences are the picture frames and the stars. They are both smaller on the Lionel car. Below notice the gap between the frame and roof line on the Lionel, while....
there is no gap on the K-Line, plus the K-Line's frame has additional detailing. The K-Line frame is closer to the correct size.
Comparing to the real car below, the K-Line frame also more closely matches the real cars in detail but a bit oversized.
While hard to see (also check above), the Lionel trucks (on right) are nicer with more definition.
To me, the Lionel car looks better but the K-Line car is closer to the prototype. I say if you already own the K-Line cars, keep them. If you don't own the K-Line cars but have been looking for them to buy, stop looking and buy the Lionel cars. They are nice.
