looking for .700 or .750 black hex spring loaded dzus fasteners car is already painted so sanding the fiberglass down to thin the area out is not an option currently

Behrents has .700" reach black slotted self ejecting fasteners but I don't see hex. You might call them an see if the hex versions are available.

https://behrents.com/pc_combin...4F41B65A0161BDB3921A

You wont find a black hex self eject. Just to make sure you are aware you can also shorten up the spring which in turn makes the fastener longer. We offer .250 springs. We also offer a .750 dome and flat head black hex, non self eject.

https://dragracesolutions.com/dzus-fasteners/