While Prototype Railroad Modeling, Volume Five won't be ready for a couple of months, I thought I'd post a teaser of one of the projects. The Missouri Pacific had a group of 100 flat cars, nos. 8000-8099, that were similar to most of the road's other cars in the 41-42 foot range, not unlike many other roads' flat cars. However, this group of cars was 45 feet in length. This is an appealing length as it falls between the far more common 40-42 and 50-53 foot lengths. After obtaining drawings from the Museum of Transportation, it became apparent that these cars could be kitbashed from two Red Caboose flat cars, confirming my suspicions.
The kitbashes also include much re-detailing, such as replacement of the stake pockets with modified Tichy stake pockets, which are close, but not an exact match, and new scratchbuilt crossbearers. The article in PRM5 will have many photos and accompanying text to help you model these "mid-length" flat cars.