Ok, now it makes sense. I was missing the context of your post.
The Cobras were not modified. They are also not 1960 vintage, but the new ones built by Shelby and Kirkham, which are tooled from the originals. The underpinnings are all stock. The original Cobras beat Ferraris on thier own turf. That is what they were built to do.
Cobras are a handful to drive. They have a rear weight bias, coupled with very high torque, high horsepower engines and a short wheelbase. You can swap the ends in a Cobra faster than you can blink, especially in turns. Trailing throttle need not apply.
The Cobra is the only American car to win the World Manufacturers Racing Cup. It did it two years in a row, but the second win (they took the top 3 spots) was disqualified, by the over seeing authority, by virtue of a rule change for the event, after the event was finished.