[rocketraider]

You actually need two pieces- the guide that snaps into the escutcheon on the headrest, and the flat clear plastic tensioner slide that fits over the belt and keeps the shoulder harness from digging into you.

Good news is these pieces are common to all 73-77 and maybe later GM cars. Bad news is a junkyard piece is probably not going to be much good. I've found both pieces on ebay but depends on who gets into the auction, they can go ridiculous quick.