I remember riders were even more weight obsessed with their bikes during the mid-1970s than they are now. This was the period of the "drillium" craze with the old Black and Decker. It would be a good idea to just look in the publications from that period for the articles on project bikes that were assembled with light weight as a goal.
As an example, the Joe Kossak articles I reproduced from the mid-early 1970s are all about exotic parts and frame weights.
Chuck Schmidt South Pasadena, Southern California (noon, sunny and 58 degrees, 45 miles west of Wornoutguy in Riverside)
> Every once in a while I come across some limited production ultra light
> weight part from the 70s. I am always amazed at what was out there is you
> had the bucks. Today everyone is weight obsessed. I want to work out what
> the lightest stuff we could build a bike with in the bike boom. I think this
> would be fun and I will put it all together on paper and forward it as a
> post. Write to me off list of what part you know of was the lightest and I
> will compile what would be the lightest thing we could build if we had
> unlimited funds. This can be as large as the frame or some specific nut and
> bolt Sam DiBartolomeo in Riverside CA for you cold climate people it
> will probably hit 80 today