HEre is on overhead view of the truck being used on the boxcar...
That Die cast spur to the left of the center bolster was threaded and used as the off-center kingpin. This was true for all those Lionel/Pola "Standard O" scale cars of the late 1970's and those that appeared in the premium scale sets of the 1980's and 1990's
BTW... Here is a pick of the NEwest "die cast trucks that Lionel Uses...
Rivited Sheet Metal with die cast sideframe bolsters