Per the "1969 Mustang Electrical Manual" (AM0028 pg 3) the Ford part number is 351453-S, strap, 2 required. However, the manual has the incorrect Ford part Number. It should be 351053-S. It is carried by AMK.
It is a legitimate use, just poorly documented.
Get a set of the Assembly Manuals for your car. You can thank me later.
Manuals are your friends.
Jim