I don't know if this was the most-recent thread, but here's a comparison of the "new" style of 73-foot Center Beam lumber cars vs the "old" style. Both are in Burlington Northern livery. The new style is on top. Inspection of the mounting holes indicates that the chassis is interchangeable with an older car. I didn't have an MTH Auto Rack handy, but I believe they use the same chassis.
This is the part number for the new car.
This is the part number for the old car.
If you're adventurous and want a 63-foot Opera Window car, there's one less opera window and panel sections on the ends are shorter on the 63-foot car. A few straight cuts, some cement and paint and you can keep the trucks at the ends of the car after cutting 10 feet out of the chassis (roughly two cross ribs worth). I know that Burlington Northern did use the 63-foot cars, but I don't know if they used the 73-foot cars later on (haven't been able to find photos). I'm not sure of the manufacturer of each car, but from the photos I've found there have been both 63-foot and 73-foot cars in the Opera Window style and 73-foot in the diagonal-braced cars.