The plastic collapsible antenna mast was what Ford expected you to use if something happened to the PM300 original equipment antenna that was supplied from the factory for the 69/70 Shelby.
FYI the picture was found on a Ebay auction that is currently active .
Yep, that is like the one I had on the shelf for 35 years and didn't open until I needed it in 2015 so I ordered a current replacement from NPD and used it until Bob G. sold me 2 of them a yr or 2 later.
TOB