Clois,
If you don't subject your Cobra to freezing temps, get rid of the
antifreeze all together, and run the Water wetter with straight distilled water.
Antifreeze reduces it's effectiveness considerably. If you do need some freezing protection, use the minimum amount of
antifreeze to your desired temp. protection.
Is your heat problem only when not moving(ie: low speed, city driving, etc), or is it regardless of driving condition? If it's the prior, most likely it's an airflow and/or capacity problem. An aluminum radiator will help considerably, along with a high volume puller fan.
Is the engine of a known source of tune? Proper timing? Proper octane for your compression ratio? Lots of variables here. How high has the temp actually reached? 200 is not so bad. Does it level off somewhere? Does it come down when you increase vehicle speed? This is all valuable troubleshooting info.
First off, try the aluminum radiator, higher capacity fan, and Water Wetter with straight water. Re-evaluate from there.
Good luck,
Dave