Welcome Kyle!
I'm afraid I don't know much about headers for an '80-'82 4wd with 335 series engine.
I do understand the frame changes from the '70's trucks might make headers for one of those impossible to fit.
Gary has a 400 in his Dad's Truck.
Maybe he has a better idea for you.
Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.