Hello, Laura.
There's a big difference between a GT40 and a 2005/2006 Ford GT (which is not a GT40). From a distance they may look similar but up close its not.
2005/2006 Ford GT comes with all the safety features you can have in a 2000+ modern car like modern brakes with ABS, even some luxury can be found like powersteering an AC. It also comes with a modern supercharged engine. All build by Ford so to be expect a finesse like a 2005 Ford car.
A GT40, GTD, is old skool, old fashion, hardcore raw. Its '60s design and mostly '60s with safety features (mostly non) and not much luxury. Well they do come with a shower cause when it raines, it mostly also rains inside.
Powersteering non, Brake assistance non, just a few have AC, but mostly underrated so on a hot day its hardcore.. with little ventilation.
GT40's where designed to be racecars. Vieuw in rear mirrors is always quest able.
There are modern build GT40 replicas like Superperformance, and Well build RCR's on the market, and even some other brands that where build years ago. But expect them all to be more hardcore. They usually come with an old skool Ford Winsor V8 with multiple carburettors requiring knowledge to maintain those.
Then there's the question how tall is the person that want's to buy a GT or GT40. Cause entering & driving it might be a challenge.
I like the hardcore raw GT40, that's why I have one.