Antenna Basket/Grommet AC Delco Part Number
 

I tracked down a GM part number for the antenna grommet used on many vehicles, including the 67-72 trucks and wanted to share since it took a while to find.

AC Delco 3820672

These can be found several places online. I just picked one up on epay for $4 incl shipping. It stretched out nice after soaking in warm water for a few minutes.
http://chuckbro.smugmug.com/Cars/196...IMG_1775-M.jpg

Btw, that should "gasket" in the title.