There's two different events at Goodwood. This one featuring all Cobras in one race is the Revival.
At the same event I hear they will have Cobras also pitted against its traditional enemies at the time, i.e. Ferraris.
AC Cobra 50th Anniversary
The date is 14-16 September 2012) and I would advise buying tickets
well in advance, they actually sell out and won't sell any more! Not like Monterey where you walks up and lays the money on the table. Oh, and Lord March would like you to dress properly (think '50s!)
Here's the website for ordering
Goodwood Festival of Speed Tickets | Tickets for FOS
Incidentally I don't have a horse in this race (though if they have a horsetrack, maybe I could enter one...)