This is actually an interesting question, for the following reason:

My impression (I am only doing gender history as part of my studies on Japanese history, so its not my main focus) is that the concept of gender was introduced into the study of history ca. around the mid-1980s, so any existence of such works in the 1970s would greatly surprise me. Amongst the publications of this time, Joan W. Scott's seminal paper "Gender: A Useful Category of Historical Analysis" [JSTOR] (The American Historical Review 91:5, Dec. 1986) is almost certainly the most-cited theoretical paper amonst historians. (Should you unexpectedly not having read this one, change it!)

The 1970s in history marked the high-point for the field of women's history (or feminist history); although some authors from these fields did already voice critique on an approach focusing exclusively on women, as, for example, Natalie Davis, who proposed:

"It seems to me that we should be interested in the history of both women and men, that we should not be working only on the subjected sex any more than an historian of class can focus entirely on peasants. Our goal is to understand the significance of the sexes, of gender groups in the historical past. Our goal is to discover the range in sex roles and in sexual symbolism in different societies and periods, to find out what meaning they had and how they functioned to maintain the social order or to promote its change." (Natalie Davis, "Women's History in Transition: The European Case," Feminist Studies 3, Winter 1975-76, pg. 90; JSTOR)

(also cited by Scott in the above-mentioned paper)

Now, I have no idea what exactly you are looking for, and therefore am not really sure why you need an author from the 1970s instead of an author writing on the 1970s who conceptualizes gender. However, if you want to find anything on gender (instead of "only" on women) in the socially-constructed sense from the 1970s, you'll have to go hunting for sociological or psychological publications—and, I suppose, Foucault's work on sexuality can be very broadly also be considered to be part of this (at least everyone who writes on sexuality in the field of gender studies has read him).

Speaking of the idea that gender is socially constructed: another book that is not directly related, but I can really recommend for having a better grasp of theory would be Berger/Luckmann's The Social Construction of Reality from 1966, since the social construction of gender is, for all intents and purposes, "merely" a specific phenomenon within these broader mechanisms. I'd really recommend reading this one sometime in your life, esp. if you intend to continue past the master's. (And, actually, I'd not be surprised if the conceptualization of gender versus biological sex is, in part, a product of the same school of thought as Berger/Luckmann's work.)

Either way, unfortunately, I'd need to go hunting myself to find such papers from the 1970s actually worth their usage in a historical study—which is a bit problematic without knowing what I'd actually be looking for—but I hope this is at least somewhat helpful. And maybe someone doing sociology, instead of history, can help you when it comes to authors relevant to 1970s discourse?