[Accelo]

The springs that return the handle are located inside the back brakes. You know the ones that make it difficult to remove the shoes? Disconnect the two cables at the adjustment under the truck. You should be able to pull on the front cable while someone releases the brake from inside the truck. This will prove the front cable function. Just pulling on each rear cable with a vise grip will prove the rears. Just pull and the springs return the cable(s). I'd bet the issue is in the rear cables as they are close to the road and crap and only last so long. The real early trucks even had a zert fitting the the E-brake cables to avoid this exact issue. I now check them every time I complete a brake job. After I smoked a set of rear brakes of course.
Nice job on the E-brake actuator. Looks just like factory with the paint going only partly up the foot pedal.
Cheers.