GGD heavyweight cars are exquisitely detailed and reasonably priced, but the details are fragile and you don't even want to think about running them on anything less than 0-72 curves. Several of mine came out of the box with details already broken off. I fixed them but it wasn't easy due to the very small size of some of the parts, giving you rather little to glue onto. Most of them have body mounted couplers, except for baggage and RPO cars which do not have end steps.
GGD's streamliners are made of extruded aluminum; only the heavyweights are plastic.