Hi everyone, first of all thanks for the great information, I realise that I'm dealing with real enthusiasts.
I can tell you that the car was built and driven in America and eventually found its way to Switzerland. I bought the car there, and it is now in Germany.
I assume that, based on your information, the interior kit was ordered, but the complete console comes from a Camaro. Just like the seats are not original. The background is that, apart from your tips, I noticed that the Firebird on the glove compartment is missing, and the console is missing.
The engine is original and has matching numbers. The gearbox has been swapped but replaced with a rebuilt one which has the same specification as the original gearbox.