When the Bluford and Trainworx cars came out, I GAVE all of my ConCors away! Chevy plants and suppliers preferred the quad door cars, and Ford preferred the twin door versions. I have a Fast Ford that I run at shows on our layout with a combination of 85 and 60 foot boxes and some auto racks. Need to make up some flatcars with vehicle frame loads from Shapeways to round it out. For realism sake, probably best not to mix/match quad and twin door cars in same block of train, unless you have Chevy and ford plant in same town on layout!
Rick