Hey Pete. For some reason the factory "J" clips for the '63 Chevy truck grille bezels require a machine screw, rather than a standard "J" nut, that requires a regular screw. Perhaps stainless or chrome is the way to go. You can find this style, by-the-piece, in the yellow slid bins at your local big box home center in your area. The tapered end is to help with starting & to avoid cross-threading, so be careful and you should be fine using them.
P.S. - I am a freak when it comes to "factory-correct" however, I have used the stainless steel, non-tapered, machine screws you listed, to avoid the bleeding onto the paint, as well as, the rusting into the fine threaded "J" nut. I have broken several of these style off in the nut, when removing, so I am for this minor, but important, improvement.
