If you find one of the old kits, buy it. They run on eBay for $12 or more a piece. Compare this to $7 or so for any other normal Walthers car and you can see there is a HUGE demand for them out there. I have only 3 but will buy any I see in the future for $10 or less.
Below is a Dean Heacock pic of a real coil car.
Note that these two hoods are rounded hoods and the hoods on my car below
are beveled. Chessie had both. Both beveled and rounded hoods
came in blue with yellow writing or yellow with blue writing. You
need some of each to be protypical. The Walthers kit comes with yellow
beveled hoods, but you could easily repaint them blue and decal them or
even buy some of the rounded hoods now available on the new rereleased
car and paint and decal them.
Assembly is straight forward for a Walthers coil car. It is much like making a flat car. Where you make your money with this car is the hoods. Weathering the hoods will make your coil car look realistic. In the pic above you see the cleanest blue hood ever (it must have just got painted) and an absolutely typical looking yellow hood. Hoods rusted very quickly, so keep that in mind.
The faults I know of on the Walthers kit are that the hoods do not come with the proper end lettering and the consolidated stencil decal needs to be replaced. I added the letters on the ends of the hoods to my cars, but did not correct the stencil. You can see a "B&O" on the left hood's end in the pic below and a "C&O" on the far left of the real hood in the pic above.
Below is a pic of one of my Walthers Coil Cars.