those appear to be aftermarket to me.
the markings on the heads are unfamiliar to me and while they used speed clips, i don't believe they're that style.
One member on the C-bodies forum said these are the same nuts and bolts that he just pulled off his survivor Newport.
This is another member from the C-bodies forum:
“Looking at them, they ARE OEM fasteners, period. Appropriate for the noted location.
Reason I know this? No replacement "hardware store" bolt will normally have a captive washer on it. Nor the under-cut end of the threaded area (which is there fo aid in the bolt finding its hole and threads on the fast-paced assy line!). PLUS that black oxide, rust resistant coating on all of the pieces of the bolt.
These bolts were fully documented in the Standard Parts section of the Chrysler and GM parts books. They usually had a minimum order quantity of 10 up to 100/package. FEW dealers would stock them, though, as there was usually some nut/bolt supplier that would supply them with "will work" nuts, bolts, flat washers, and the related clips. BUT, if one was wanting the OEM-correct items, they could be ordered.
The slide-on clip is OEM also. Not specific to Chrysler, but to all OEMs who used such a clip/nut.
In the parts book exploded views, whenever a bolt or nut is referenced in the illustration, it can be referenced in the normal parts listings. THEN take that part number and go to the Standard Parts section. There will be each type of bolt detailed with a factory part number on it. Size, thread pitch, captive washers and such, coating, bolt end type, Grade markings, etc. ALL in engineering-style illustrations. In all of the lengths and diameters for that particular style of item AND with the factory part number and min order quantity listed. Very NEAT!
Now, the OEMs were using parts from an outside vendor, which would be packaged in the appropriate OEM packaging when the dealer ordered them.
Just as with many OEM small parts, with time, the older items will be deleted from the newer catalogs. Yet they can still be available from the suppliers, if they can be determined. Which can be important as the older salvage yards are "crushed-out" for various reasons.
Lowe's and other hardware stores CAN have some of them in their nut/bolt aisle selection, but the selections can vary. As can some of the body shop nut/bolt suppliers.
Over the decades from the 1980s forward, some vendors have begun to sell "bolt kits" in the restoration end of things. One Mustang parts vendor started to get into this industry, with nut and screw kits. We'd see him at Mopar Nationals doing research, for example. At that time, the main thing that was of concern were the smaller, chrome plated, Phillips head screws (which could be easily dropped and lost in the shop or vehicle. Those screws were also in the Standard Parts OEM catalogs, too. Obviously, he had found a source for these things, but I always questioned how accurate his kits were (never bought any of them myself or knew others that did). I have seen few kits which have the correct, oxide-coated bolts and such, in the "restoration industry" kits, using normal "silver" bolts and nuts instead.
IF you might happen to see a "nut and bolt restoration", look for the oxide-coated bolts to see if they are there or not! Most times, you'll see the normal "silver, hardware store" bolts and not the black oxide fasteners the vehicle came with.
Just some observations from decades in the dealership car parts realm of things,
CBODY67”
