This is the 3-bogey inner bolster assembly to the third in a series of high capacity
depressed center flat cars using bdneals 8-wheel buckeye trucks (kuid2:96914:50195:3)
which can be downloaded from his site (Subpar Productions) in the 2-6-6-6 common pack.
Many thanks to him for letting me use them. See New Hi-Capy Flat 3 Body (kuid2:210516:6574:1)
for assembly instructions. The screenshot shows the assembled traincar.