Carsten,
Try this site
http://www.racingsportscars.com/cars.html
and go to the advanced search at the bottom of the page.
Enter Shelby as the Make and Cobra as the Type and you will receive many pages of Cobra race results, but you will need to sort through which are the 427s. You can also use A.C as the make and will get a few more CSX3*** cars that were not shown on the Shelby pages. Probably not all inclusive, but it is a start if you have the patience to go through the pages.
Jay