Any idea what the thread size of a 59 GMC sector shaft might be?
I believe the sector shaft thread is a 1/2"-20, or a 5/8"-18, not sure which. I'd suggest getting one of the thread repair files and trying to clean up the damaged area at the top of the thread, even if you choose to chase them with a die afterwards. It's essential to remove the bulged area at the top before a die will engage the existing threads and follow along the same track as the original thread. If you've got a few good threads near the bottom, all that's necessary is to clean up the top enough to get a new nut down to the remaining good threads. Good luck!
Jerry
