bycycle or trycycle License plates and frame and bracket

made this is for my Kaz adult trike there is another company that is selling adult trikes now the plates are 3x6 most standard bike plate the frame should fit custom plates on ebay the hole pattern is form one don't know for sure about all but a good drill can fix that
there seems to be no standard bike plate sizes if somebody knows what that is i would like them to inform me so i can adjust the hole pattern to match so far i have found 5 different hole and size patterns that claim to be stand