If it were new it would probably stand the pressure and probably even reject plenty of heat, but 68 years of water/antifreeze that has anything but a neutral pH will cause weak areas that will fail, usually on the hottest day of the year and as far from home as you ever will be. Murphy's Law number 4 says: "If there is a possibility of several things going wrong, the one that will cause the most damage will be the one to go wrong. Corollary: If there is a worse time for something to go wrong, it will happen then. "

As Dave S. says, there are too many better alternatives - copper or aluminum - take your choice, to take a chance