The Weaver PS-1 cars are scale width and length for PS-1s - Pullman Standard etc. They are pretty much the same dimensions as the 1937 ARA car which Intermountain/red caboose made. The the 1937 ARA is a model of a car with Riveted side assembly while the PS-1 is a car with welded sides. I think the whole PS series was a set of cars that Pullman Standard designed to be welded not riveted, including the gons and covered hoppers.
Weaver also picked up the molds and issued a 40 ft car that is lower in height. This model is made from the original Crown Model Products molds. It is a model of a much older car I think, a 1923 ARA car. It is still a 40 ft car but I think the interior height was 9 ft or 9 1/2 feet as opposed to the PS-1 which 10 1/2 feet. The 1923 ARA car is basically the same dimensions as the PRR X29 which Atlas did/does the very nice model.
I don't know anything about the stockcars, I never had any. I did have a few of the weaver reefers and the OSB boxcars. The reefer are lower height wood side cars. The Outside braced boxcars are based about the same dimensions as the 1923 ARA steel car. They are based on a slightly more modern prototype than the USRA cars. The rib spacing is wider. There was an article in one of the magazines some years ago that described those particular OSB cars and who had them etc.
All in all, the Weaver cars seem to be scale size and based on real prototypes. All the detail is cast on. rather than add on. Lionel bought some of the Weaver molds and came out with the "Lion-Scale" line using those bodies.