The 40 in the car's name is a reference to its height, which was 40 inches measured at the windshield. The engine was a 4.7L V8. The Ferraris it competed against at Le Mans had V12 engines.
The original GT40s made by Ford were just called the GT. Ford would later introduce an homage to this vehicle in 2005 using the same name.
If you want to buy an original of these cars, good luck. You'll have to find a private owner who is willing to sell, and most of them are superrich and have no need for your money. There are at least a dozen kit cars that are replicas of the original GT40, however. You can buy them for a reasonable price, and then you won't feel bad about dropping a huge non-original engine it to get insane amounts of horsepower. Try looking on eBay for these. You can also find some pretty cool collectibles for this car on there.