Didn't Mango do his own rear trailing arms? I thought it involved flipping them side to side and notching or sectioning.
Pretty sure he documented it here.
As I recall, you can't make them narrower than about 3/4" on each side—1.5 inches total.
Correction: 1.2 inches per side.
Here's @MangoSmoothie.ca selling a set he made 11 years ago...his last.