Captain Marvel & Mary Marvel from proposed Shazam! reboot by John Byrne. 1989.
From Back Issue #12, as quoted by Brian Cronin at Comic Book Urban Legends Revealed #99, John Byrne on why it did not happen.
The reason this [project] didn’t happen was that going in, I said I want this to be a separate universe. I want this to be not connected with the DC Universe in any way. And DC said, yep, fine, that’ll be great, that’ll be good. And then I had actually done the cover and the first two pages of the first issue and they said, “Oh, by the way, Cap has to be in the Justice League [Here, Byrne most likely just means that “Cap has to be in the DC Universe, as Cap’s Justice League days were past by this point].” And I said no, we agreed. And they said he has to be, it’s absolutely necessary. I said, well, bye then. It was another one of those cases where I made my unreasonable demands loud and clear, up front, they agreed to them, and then said, “Oh, no, we’re changing our minds.”
Below the character drawings are the two pages John did. The first image was used for the first page of OMAC #2. John explained on his website:
The first page, as some of you may already know, was salvaged from my aborted SHAZAM project. When DC double-crossed me (this time before the contracts were signed!) I pulled out of that project and took back the work I had done on good faith. When I needed a splash for the second issue of OMAC, I did some cosmetic surgery, removing characters and altering the vintage of the automobiles, and what had begun as Fawcett City became the setting for Buddy Blank’s adventures in the Past.