AFAIK all Chrysler Corp seat bases were supposed to have these plastic spacers. One of my bucket seats had them, and one didn't. The one without had rust on the seat base from carpet contact and moisture in the carpet. One would suspect that seat belt testing was done with the spacers and therefore specified for all seat bases.
They can be easily and cheaply made with PVC pipe fittings turned on a drill motor or lathe. They are also virtually invisible and mostly unnoticed.
Parted a few back in the day, mainly e-bodies, & NEVER saw any installed.
Only a 69 Charger.
E-bodies had crappy headroom without them in to start with.
