FYI, I have built this kit. The basic car is cast metal. The weight makes it useable.
Theprototype and the kit mount three couplers on each end. The center coupler of each set is set to use with standard gauge equipment. The two outside couplers are set to couple ng equipment. It gets a little tight, but doable.
My efforts predate the new Kadee narrow gauge coupler. I'm not sure how it would help or hinder the three coupler arrangement. If anyone does such a setup with the new Kadee I would appreciate hearing how it went.