Replacing Letraset's own Super Action Transfer sets with licensed characters, there were three ranges of Super Action Heroes…
(You can select individual sets from the thumbnails below, but for the full experience we recommend using the "Get started" link when you get to the bottom of the page.)
GK173 (1974)
GK217 (1976)
GK245 (1977)
Here is a full-page ad for the series (& for the "Super Friends" range), taken from 2000AD Prog 41 (3rd December 1977). Note the reference to the "Letraset Toys Club", which unfortunately we have it from the highest authority was so unsuccessful that no-one can remember it having ever existed:
To give you an idea of what these sets looked like before they were opened, here's the front & back of the "Tarzan of the Apes Battles the Catmen" set, still in its wrapper:
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