That sucks!
My wife has "421GOAT" on her 65 421 Tripower GTO, and I already posted the "6PAK440" on my Roadrunner.
Antique plates in Louisiana are LIFETIME plates, so pay once and never again. About $38 for the Antique part and I think it was $100 for the custom letters/numbers.
Also any car or truck with an Antique plate NEVER needs a "brake tag" or "inspection sticker" so NO emissions testing. I could be burning nitro methane!