There was also an issue of Shazam! back in the '70's where Billy wore a turban with a jewel in it and that jewel deflected his lightning so it struck, among others, Mr Morris and a chimp. They also didn't become "the dark-haired, very male Cap we all know".
I seem to recall an issue in a 1940s collection where someone else was accidentally struck by the lightning bolt and THEY, not Billy, became Captain Marvel...but this may be the issue equivalent of that comic where Thor survives inside the sun, or Superboy and Krypto use “telepathy” on each other.
According to Ordway's TPOS series (which had it's good moments), the power of Shazam gives Billy (or Mary or Freddie) super powers and they become an idealized version of themselves, either consciously or subconsciously. That's why Mary doesn't become "the dark-haired, very male Cap we all know" and Freddie still looks like himself as Junior.
An interesting concept, but if people turn into idealized versions of themselves, why would Mary Marvel turn into a teenager instead of a woman?
And though I’m not generally a fan of the SHAZAM! guys, Ordway is an incredibly gifted artist, and the whole series had a wonderful sense of humor. My favorite part was this interaction:
CAPTAIN MARVEL: “Why...you’d have to be thousands of years old!”
BLACK ADAM: “Yeah...and how old are YOU?”
Or “You betrayed the wizard Shaz…uh, you know his name!”