1968 Dart cooling system & gauge Questions

Back in the day, we used 8 lb caps with a 50/50 mix of antifreeze. The mix has a boiling temp of 265* plus whatever the cap increases it by. My relatively stock 340 runs at 180* all day long with no pressure in the upper hose. As a matter of fact, when I SLOWLY squeeze the top rad hose, I can hear the cap venting.