How about the Clasic Roadsters Cobra? Have you had the chance to check them out? They have a very rigid frame, great suspension options, and a 6" steel safety rail in the (functioning) doors. It has a Great fit and finish, and I have seen statistics of Great performance on and off the track! Call them and get some info, or check them out on the web at
http://www.classicroadsters.com/
Check them out. They have been in business for 26 years and have stood through the test of time!