Hi scubamom,
This depends to some degree on the type and blend of the latex, the firmness of the layers, and on the design of the mattress. Some latex mattresses will become softer over time (generally a long time) and others will lose some of their resilience or height and become firmer. Synthetic latex can become firmer or “stiffer” as it oxidizes and in some variations can lose height more than natural latex which tends to become softer over time.
It could have been either natural Dunlop or Blended Talalay since both were in fairly widespread use in the 70’s (see post #9 here). You can see an example of a Dunlop mattress that was almost 50 years old in the video here.
Phoenix