Then I would say it's most likely a past owner put that badge on your Bronco from a Mustang. I'm not aware of Ford ever offering a "Sports Sprint" option on the Bronco.
On the plus side, those emblems are pretty rare now. You could probably sell it to someone restoring their '67 Mustang Sprint.
https://www.ebay.com/itm/1761812197...d=link&campid=5335857059&toolid=20001&mkevt=1
Edit to just add that there's also a slight possibility that the dealer added these to your Bronco. Ford did all sorts of "special editions" in the late 60's, most of which were just cosmetic. And some of these special packages had pieces that the dealer was supposed to install once the car arrived on their lot. There are plenty of stories about dealers slapping on emblems, stripes, wheels, etc onto cars they were having a hard time selling. It's possible that your '66 Bronco had been sitting on the lot for a while and when the new '67 Mustang "Sports Sprints" came out the dealer took some extra emblems to "dress up" your Bronco.
I still say it's much more likely a previous owner did it, but the dealer story is a fun one to imagine.
