If your road runner (or any '69 Chrysler automobile, trucks excluded) had a Scheduled Production Date (SPD) of December 1, 1968 then it was to have the "head restraint" hardware already installed into the seat backs. Only the bezels and head restraints needed to be installed if requested or needed after January 1, 1969 when head restraints became mandatory due to the 1966 Federal Motor Vehicle Safety Standards or FMVSS. The phase-in for the safety standards started 2-years after the regulations were voted in so 1968 model year cars started to see some of the regs come on the cars like the side markers (lights then reflectors and then lights/reflectors), rocker switches or recessed switches, padded dashes, glove box doors that were padded and closed on impact, collapsible steering columns, non-reflective/low-glare, horn rim, mirror assemblies, column shift levers, turn signal stalks, etc. The inside rearview mirror was to be breakaway or movable and the inside door opening handles designed not to be of a type that could be snagged by occupants and unintentionally open. The window crank handles even hand to have the knob made of breakaway plastic. The seat backs had to have a locking device and a latch to fold them that at first was at the bottom rear and eventually moved to the outside, side of the seat back. Seat lap belts were first then the 3-point belts became mandatory but Chrysler decided to do the 3-point belts sooner then required by law. Heater, well actually a defroster system for the windshield became a standard safety feature and even the VIN being placed in a position on the driver's side and "visible through the glazing" was part of the FMVSS regulation. The visible VIN was deemed a safety regulation so it would help law enforcement with checking vehicles when stopped or parked to see if they were stolen........the regulation even explains how studies had shown that stolen vehicles were more likely to be driven unsafely, not making that up. If you ever get a chance to read some of the FMVSS regulations (I've had to for the past 25-years as my job) you'll understand more why cars are designed like they are and why fatalities dropped dramatically per miles driven and number of vehicles since they became law. They made a pretty big deal about them even on the "window sticker" (Monroney Label) starting in 1968.
Lots more from hood latches with the safety hook (still wondering how the A12 Lift-Off-Hood sidestepped that one but then again it had 4-hood securing devices LOL) to the oval gas filler hole in the later '69 road runner B-bodies so the filler neck had less possibility of being knocked off if hit in the rear quarter. Side impact door braces in '70+, safety glass, etc,.............the FMVSS regulations "impacted" (pun definitely intended) the way cars and trucks were designed and built from that era on......................and then the EPA era piled on too, that's another story.
MikeR
