This set was produced to introduce a more comprehensive set for these classes, which hadn't been done by previous manufacturers.
The majority of the PRR's Wreck Derrick fleet was built by Industrial Works, later Industrial Brownhoist. There were four major classes of derricks used post-1900, W100, W120, W150 and W250. With each came an increased lifting capacity. The W250 were required after purchase of the J1a locomotives in 1945, all were steam powered and self-propelled. In addition to these major classes, each one had subclasses based on the length of their booms, please refer to Rob Schoenberg’s site showing diagrams of each class. http://prr.railfan.net/freight/PRRdiagrams.html
This sheet includes enough decals to decal 3 Wreck Derricks with two correct numbers for each car class. The number jumble contains all three of the 4 number prefixes (4907, 4957, & 4909), with an additional jumble to cover any number accurately seen in photos. Also, a jumble is included for making your own derrick weight, which also varied through the service life of the derrick. See the diagram for proper placement.
The W120 (kitbash-able to a W100 or W150) class is produced in plastic by Tichy. The W250 has been produced by Athearn.
For references in regard to the PRR's Wreck Derrick Fleet, please consult PW&B, PB&W and PRR Company Service Cars, compiled by Richard E. Hall and published by the Wilmington Chapter, National Railway Historical Society, and Volumes 1-3 of the PRR Color Guide.