In Alter Ego #37, comic book historian Will Murray hypothesizes that The Secret of the K-Metal was intended for one of three different possible comic books:
Either an issue of Superman (either issue 7 or 8, most likely issue 8); an issue of Action Comics (most likely issue 31) or as the lead feature in a possible new, third Superman title. He states that Superman #8 and Action Comics #31 would have both been cover dated December, 1940; presumably the third new Superman title would have also had that date.
Of the three possibilities, he considers the Action Comics #31 option to be the most likely. This was our first try at a cover:
The primary cover that we used for the first stage of the restoration project was based on the Superman #8 possibility, although we used the same Jan/Feb 1941 cover date that DC’s published Superman #8 carried.
as were Angel’s early cover drafts
After the first stage of the restoration was complete—meaning that we had a complete, full color comic book with no missing pages— the story was “officially” released as Superman Through the Ages! issue #0:
This is a mixture of restored original artwork alongside new, contemporary artwork. Future “stages” will involve restoring additional missing original pages as they are discovered, with the hope of eventually recovering the entire collection of 1940 Shuster Studio pages to present the complete original comic book consisting of all the original artwork.
Stage one of The Secret of the K-Metal may be read online here.