In the 1950s and to some extent through the 1960s aluminum handlebar stems a seat posts were not as good as they are today and were prone to breakage. So back then people rode bigger frames with less seat post showing and they used a shorter handlebar stem so a longer top tube was called for.

By the 1970s handlebar stems were available in much stronger drop forged aluminum; seat posts too were better. The result was frames got smaller; (More seat post showing.) top tubes got shorter so with a longer stem the rider’s weight was more over the front wheel making for much better handling.

These old frames generally had shallow head angles, long fork rake, and a long top tube. This in turn made the seat angle very shallow around 70 or 71 degrees. This is what people usually mean by a relaxed geometry; or more ‘laid back’ for want of a better phrase.

You are right in your assumption that with your bars low and sitting so far back your hips are restricted and my advice is to raise your bars a little at a time until you can find a position you can live with. And you will have to accept the fact that with a frame this old you are never going to achieve the same riding position as others on their newer bikes.