Check out Roger Kraus Racing for tires for your Cobra.
http://www.rogerkrausracing.com/Cobra/
You should consider the Goodyear Billboards ("tire B" on the website), or the Avons ("tire F" on the website).
You can search the forum to find more information/opinions on these tires.
The Billboards look great, but are a bias-ply tire.
The Avons are a V-rated radial tire (probably about the best all around performing 15" tire available for Cobras).
Good luck.