When I first read of American OO model trains being 1/76 instead of 1/87, which was what I had worked in mostly to that time (HO), I was very curious to actually see the comparison. I had purchased a couple of items in TT scale (1/120) in this time frame (late 1970s) from a company located in Hungry Horse, Montana, the Eastern Model Railroad Company. This company had actually started out as an OO gauge manufacturer in Hackensack, NJ, in 1946. Their line featured three cars, a 40' steel boxcar, a 40' reefer with steel or wood sides, and a 40' gondola. He still had old stock of the boxcars at that time and I purchased one and built it, the car on the bottom in the photo.
The other car is one of my original HO cars, a 40' boxcar by MDC. it gives a good comparison of size; OO is bigger. Click on the photo for a larger version.
Back to the Eastern car, there are a couple things to note about this craftsman kit with printed card sides and cast details. First, the trucks look like Scale-Craft trucks from the side but they are a little shorter in wheelbase and have a different bolster. The second would be that perhaps 80% of the parts are identical with those on a Famoco boxcar (including these trucks), and the production of these models actually overlapped. This is one of the mysteries of OO history. The sides are the same; the two main things that are different are the two models have different frames and the Famoco version has cast ends instead of pressed card ends. J-C Models passenger cars also share about 80% of their parts with Famoco and production overlapped; the J-C version has no metal parts while the Famoco has cast ends and other metal details.
UPDATE: My overview article on Eastern OO is here.