Looking underneath the Herbst TT, the trailing arms look like many others I've seen, with one exception.
The links are not adjustable. Most of the time, the rear pivot is a heim joint that can be threaded in and out in order the square up the axle under the truck.
If you can square up the axle under the truck without needing an adjustable link to accomplish it, you can use uniballs at both ends. Since uniballs don't have a threaded shank they do not put a bending load in a threaded shank.
What's the big deal? Threads are indentations and thus are potential failure points. Under a bending load, uniball assemblies are stronger than heims.
Uniball cups cost less than the threaded housings used on heim joints. Furthermore, you won't need a weld bung in your trailing arm. Fewer parts mean less weight.
Finally, fewer parts mean lower costs.
Since most trucks don't have identical frames due to manufacturing tolerances, it's still a good idea to build trailing arms with heims if you're building something mass produced and you want user friendliness. However, if you're building something one-off and custom, uniballs at both ends of the trailing arms have some distinct advantages.
It was also worth checking out the frame end mount, and the boxed structure that makes up the foundation for the rest of the chassis.
This truck is truly a thing of beauty.