Until recently, this car was not included in the list of cars that had been found in Gilbert Kleer Paks which were used in the Pikemaster era from 1961 - 1963.  See an Illustration of one such car below.  (As a 33511, it is only cataloged from 1958-1960)

According to the Charles Sommer Guide to Gilbert HO, 1960 versions of this car, like may other freight cars of that year, had solid metal unsprung trucks.   The trucks  bear the number P15D396  The Kleerpak car below appears to have such trucks.

511  -  Daryl Olszeski Collection

33511  -  Daryl Olszeski Collection