For anyone who wants to model the NASA space shuttle train, but does not require all the SRB sections and support frames, here is a cheaper alternative. It's the clamshell covers, but printed as a 1-piece part, with the alignment brackets created as part of the model. The part will need preparation before painting/decalling, and can then be fitted to the Walthers 66' four-truck, heavy-duty flatcar.
If you require decals to complete the model, please contact me.
A fellow designer, HODiver, has created the Heavy-Duty 8-axle flatcar deck & truck-mounts, if you are having trouble obtaining the Walthers version. Please see the links below and visit his shop.
https://www.shapeways.com/product/U742EQ92F/66-heavy-duty-flat-car-walthers-design?li=search-results-1&optionId=58755784
https://www.shapeways.com/product/EBX79WBW2/truck-mounts-for-the-hd-flat-car?key=1e99a94c1c131a4980b9dcdc94a30970