Yes, Leloup was responsible for the design of the plane. As you say, Jock, it's most likely that the design is a pastiche of various sources put together with Leloup's technical know-how.
According to the book Tintin : Grand voyageur du siècle
, the plane in existence today that is most similar to the Carreidas 160 is the Falcon 200
. A bit of research suggests that the '200' was a modification of the Falcon 20
, whose prototype was built in 1962. The '200' had a few changes made to it, but since it was unveiled in 1979 that puts it out of the timeframe. It's very possible that the '20' inspired Leloup in the creation of Carreidas' jet.
What we know for certain is that Laszlo Carreidas was based on Marcel Dassault, the head of the company responsible for the Falcon, amongst others. There's a short biography of him here
, but if I can draw attention to this passage :
"Besides his work in aviation, newspapers and politics, Dassault was keen on architecture, cinema, banking and the stock market."
But to get back on topic, if we're going to pull the Carreidas 160 apart to identify source elements, I think it'd be best to use the technical drawing by Leloup which features in Tintin & the World of Hergé
in addition to the album, since it gives us a nice cutaway of key parts.
Note from Jock123:
Richard - I took the liberty of changing the links for the ’plane pics above, because the host site wasn’t allowing the link to be used directly to the photo (it did work if you copied the url and pasted it into a new browser window); however, by tracking down the photos used on airliners.com, I saw that the banner above the picture contained a url to use as a link, so I have sorted that here.