In the past I've read about plate brackets that were vacume operated.they used the vacume motors found on oem air cleaners. I used to have a 56 Bristle I made a hinged and sprung plate holder that layed down at speed. Iowa 1971 era. I now have a EM in Washington .My plate lays flat attached to
oil cooler duct in nose.
Remember when the originals were done front plates were used so parking meter maids didn't have to walk around to rear. They have photo radar and the like now.They tried Photo radar and the red light stuff here . I twas a cash cow for Lakewood for a while. When the grants ran out and some of the tickets were reversed they abandoned it all.I think the only time that front plates are an issue is when they are using photo ticketing. It allways revolves around money.Cobras arenot beaters and anybody driving one is likely to pay a ticket,cha-ching.