Need help identifying interior part
 

I just finished reassembling my 04 G35 coupe's interior after replacing the sunroof, but have now two parts left over that I'm having trouble identifying. They're identical white plastic blocks ~2"x1"x1" (see image). If I had to guess, I would say they belong somewhere underneath the A pillars. But if they do, I can't figure out exactly where, or what purpose they serve.

I tried looking them up by the number embossed on them (73991AL500), which I would assume is their part number, but found nothing. Any ideas? Thanks in advance!

Goes in head liner which is used for the support of the grab handles

Thank you thank you! That makes sense. Come to think of it, the bolts to attach the handle did seem to take an inordinate number of turns to screw in tightly!