This only my speculation, but I think what you have there are known as “swing motion” trucks. The indication is the fact that the elliptical leaf springs are set somewhat to the inside so their centers are inward from the centers of the side frames.
The truck bolster is attached to the tops of each leaf spring by a connecting casting of some kind. The bottom of each leaf spring is attached to the spring plank with a similar casting.
However, the spring plank does not mount solid in each truck side frame. Instead, the spring plank is suspended by
spring plank swing hangers that are attached to the solid cross members that connect to the side frames and are positioned on each side of the truck bolster.
The spring plank swing hangers are mounted with a hinge pin that allows them to swing in arcs crosswise to the truck. This allows the spring plank to move side to side. Because of the arc of the swing hangers, when they allow the spring plank to swing to either side, the spring plank lifts slightly. So when the force that is acting to cause the swing dissipates, the hangers naturally settle back into their centered position.
If you look at the photo of the EBT truck, you can see the tops of the spring plank swing hangers on each of the solid cross piece timbers, on each side of the bolster. So, there are four of these swing hangers. They also require special castings to attach them to the bottom of the spring plank. And those attachment castings must have a pivoting connection with a pin so they have a hinged attachment to the bottom of the spring plank just like their attachment to the solid cross members at the top.
So you need four swing hangers, four pivotal swing hanger mounting castings at the upper end of the hangers, and four pivotal swing hanger mounting castings at the lower end of the hangers.
And you also need a mounting casting at the top of each leaf spring that attches it to the bolster, and another mounting casting at the bottom of each leaf spring that attaches it to the floating spring plank. Perhaps these top and bottom spring mounting castings can be identical.
