These cars are modeled after the Iron Mountain coal cars that Accucraft produces in 1:20.3. They are designed to accept Kadee 26" Hon3 wheelsets which simply "snap" into the journals. The cars run very smoothly once assembled. They are designed to accept Kadee 714 couplers or Sergent Engineering Couplers (as shown in photo).
The updated version has the upper extension on the "bin" itself and brake detail built in to the end beam where you'll spot the brake wheel post and some added nbw detail per the prototype.
To finish these, a piece of .040x.015 styrene is secured on the end beam inline with the journals and then glued with CA to the bottom of the journals and back up to the end beam on the opposite end (See photo). I used Rio Grande Models brake beams on the bottom and sergent couplers.
I painted the model with a mix of thinned 75% floquil roof brown and 25% floquil antique white in an airbrush. Then painted the metal parts floquil grimy black and weathered with powdered chalks.
They're sold here in a 5 pack to save you money (shapeways charges a $5.00 fee for Frosted Ultra Detail per order, so by ordering 5, you spread that cost out across 5 models. You can also buy a kit from http://www.lightscalemodels.com
which includes the wheelsets, styrene, brake beams, brake wheel and brass wire for the brake wheel post.