Gillette did make a Tech with a diamond shaped base and the bar on the underside of the top cap ran the length of the cap. Yes. 1960s, I believe. The Tech is a great razor! It doesn't nip the blade up quite like these Star razors, though. Most certainly the definitive DE shave, but still has that little blade chatter and just a tad too much exposure for the blade to feel absolutely rigid.
There do seem to be a lot of Star razors in a very tatty state. Annoyingly, some of the better looking examples (certainly top caps) have aluminium base plates and handles. They're the later ones. I'm not sure what you mean by pot metal - are we looking at the same razor? Do you habe an example? The Star and Treet razors that I have, Personna and PAL too actually, feel to be of a similar build, weight and quality to Gillette of the same era.