i recently found a 454 tbi at a wrecking yard that was missing the injector pod. so i went back looking for one. i fouund this, as i recall, on a '80 cadillac 6.0. it appears to adjust spring tension as the diy afpr does. ( correct me if i'm wrong)

another...

Yep the 368 DFI injected and 8-6-4 cadillacs are adjustable. I think they are adjustable for the older RWD 4.1s too. The later ones would be too, had GM not welded them into place. I have broken many of the welds to bring the fuel pressure up to 14-15 psi, on alot of GM tbi engines.