Lud is correct in his observations that this is true with all aluminum engines/aluminum heads. They react very badly to overheating, even for short periods.
If your coolant system is pressurizing, you need to find out why. The head gasket (s) is the first obvious choice. If one is failing, you will probably see signs of it with a visual inspection, but replace them both even if they look good. Also, have the heads checked to make sure they are still true and mill them if they are not. Then, pressure test the motor BEFORE you put it back in the car. Nobody does this, but it is a very important step. You do not want to have to pull the motor two days in a row (ask me how I know).
A couple of weeks ago, a friend and I pulled my motor and completely disassembled the heads in about 3 1/2 hours. Its a pain, but think how much easier your header installation is going to be. ; )
Also, if you drop the motor, do any engine service that might be due in the next year or so (t-belt, heater hoses, clutch, etc.). You will be glad you did later. For example, installing the headers takes about 20 leasurely min. with the motor out of the car. T-belt takes about 10 min. to install and index with the motor out.
Good luck.
[This message has been edited by David (edited 29 December 2002).]
