Easy, cheap, third brake light

If interior mounted fixture doesn't hug up tight to the glass the leaking light blinds the view out.
Models with pretty much flat and vertical rear glass are easier to fit and shield than others, like B'cuda for example.
Then there is usually a wiring/blinks with turn signals issue to resolve because these classics have combined brake/turn circuitry. Simple solution there is about 20 feet of white wire tapped into white at brake lamp switch and routed along left rocker with factory wiring all the way to the added fixture. Good luck to all.