I graduated from HS in 1971, and we took a non-PSAT NMSQT. IIRC, there were something like 5 sections/subscores, and the content of some was more “factual” than the PSAT. Possibly it was more like the ACT, but I’ve never taken that one, so I don’t know.
There was, AFAIK, no possibility of prepping for it. You just went in one Saturday and took it. Of course, prepping for the PSAT/SAT was unheard of then, at least in my circles.
I think we may have been the last class to take the separate test. I do recall that there were different cut-off scores by state.