I grew up in miami Fla & we had royal castle. It had an orange logo.
we used to stop on the way to the beach and my dad would get a box of them little suckers. And the birch beer was a must with the burgers. i remember back in the early 70s they rolled the price back to a nickel a hamburger, man did we load up! Three was about how many I would eat at one time.
i miss them so much, ( live in Az now ) I make a version of my own.
I’m sure mine has much less fat in it, but just dice some white onion really fine and make your burgers thin & small. Then steam the burger on top of the pile of onions. Get some hot dog buns and cut them to make your burger buns. then 3 pickles, ketchup and mustard and you got it. it’s not the same but damn close.