You would do well to look at the Toto line. The Willingham model is one good possibility, there may be others that would fit. You are really coming out of the Dark Ages if your old beast is 70 years old. It is likely a 5 to 7 gallon per flush water hog and you will be moving into the 1.6 or even 1.28 gallon units. You need to understand that although every toilet on the market has to meet these standards, no choice in that, all brands do not work as well as others. Many of the big name brands of the past are still trying to tweek the old designs to make them compliant. Toto completely redesigned their toilets so all models perform well even with the small amount of water requirement. Toto is now the largest toilet manufacturer in the world largely because of this.