Hey! Thanks very much for this, which I just now discovered.
Several years ago, I posted a query to Larry Talbot about stories where
Sivana steals the magic lightning bolts, swearing that I once read a
Golden Age story where Sivana manages to intercept the lighting and
transform into Billy Batson into "Captain Sivana." (There's an easily searchable
reworking of this idea that was published in the 1980s, which people
cited when I brought this up, but I was sure I read it first (and was terrified
by it) as a six or seven-year old kid.
"The World of Too Many Sivanas," chapters 3 & 4 in CMA 150 is it!